What Information Does a Private Investigator Need to Catch a Cheating Partner?
If you’re reading this, you’re probably not killing time over a cup of tea.
More likely, you’re staring at your phone late at night, replaying conversations, second-guessing your instincts and wondering whether you’re imagining things… or whether your partner is actually cheating.
When you add narcissistic behaviour into the mix – gaslighting, blame-shifting, “you’re crazy” comments – trusting yourself gets even harder.
For some people, hiring a private investigator for a cheating partner becomes the turning point. It’s not about being dramatic; it’s about getting something narcissists hate: evidence and clarity.
In this guide, you’ll find:
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What information a private investigator (PI) actually needs
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How tech, multiple numbers and AI make cheating easier to hide
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Why narcissistic cheating behaviour thrives in this digital mess
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How to protect yourself and your privacy through the process
No fluff. Just straight talk so you can make informed decisions.
Why Hire a Private Investigator for Infidelity?
First things first: you are not “paranoid” or “vindictive” for wanting answers.
Cheating – especially when it’s tied up with narcissistic traits – can:
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Shred your sense of reality
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Trigger old trauma and attachment wounds
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Blow up finances, living arrangements and future plans
Because of that, a private investigator for infidelity can play a very specific role. They aren’t there to tell you what to feel. Instead, they:
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Observe real-world behaviour
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Record what actually happens (not just what you’re told happened)
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Provide timelines, reports, photos and videos you can use for closure or in legal settings
However, even the sharpest PI cannot read minds. To avoid wasting time and money, they need you to come in with clear, accurate information.
Before You Call a PI: Quick Reality Check
Most people don’t wake up one day and randomly google “how to catch a cheating partner”. They usually reach that point because:
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Something feels “off” but they can’t pin it down
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They’ve seen troubling signs and been gaslit into doubting themselves
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They need proof for separation, custody or property settlement
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They’re desperate to know they’re not losing the plot
You don’t have to be 100% sure before you speak to someone. What helps far more is being organised and honest about what you’ve already noticed.
1. Core Details About Your Partner
Let’s start with the boring but essential stuff. A PI needs to know exactly who they’re watching so they aren’t fumbling around in the dark.
Try to have as much of this ready as possible:
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Full name, plus nicknames they actually use
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Date of birth (even just month/year is better than nothing)
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Mobile number or numbers – including any “work” mobiles
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Email addresses – personal, work and any “spare” accounts you know about
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Home address and work address
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Usual work hours and roster or shift patterns
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Vehicle details:
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Make, model and colour
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Number plate
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Other vehicles they regularly drive (work ute, motorbike, friend’s car)
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In addition, recent photos help a lot. Different angles, with or without glasses, and in work clothes if relevant, make it easier for the investigator to confirm they’re following the right person.
Example:
“We’ve been together 8 years. He works at a warehouse in town, officially 7am–3pm, but lately claims he’s staying until 6 or 7 ‘to help out’. Drives a black Mazda 3, plates XYZ-123.”
The clearer you are here, the smoother (and cheaper) the investigation becomes.
2. Your Relationship Snapshot (Why Context Matters)
Next, your PI needs to understand what “normal” used to look like for you both. Without that context, changes in behaviour are harder to spot.
It helps to explain:
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How long you’ve been together
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Whether you live together or separately
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Whether you’re married, de facto or engaged
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Whether there are kids or step-kids involved
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How responsibilities are usually split (school runs, housework, bills, pets)
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Any big shifts in the last 6–12 months:
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New job, gym, hobby or friendship circle
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Sudden health kick or intense self-improvement phase
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More travel, work trips or “work functions”
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On TheNarcSlayer.com, we see this pattern over and over with narcissistic partners. They build plausible cover stories – “I’m focusing on my career”, “I’m finally looking after my health”, “I need more freedom” – while quietly rearranging their life behind the scenes.
Once your PI knows the baseline, they can identify where your partner’s story stops matching their actual behaviour.
3. What’s Actually Making You Suspicious
This is where you drop the “I don’t want to sound crazy” act. You’re not in a courtroom; you’re giving the investigator raw data.
Instead of a vague, “He’s just acting weird,” be specific about:
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How he or she has changed
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When you notice it most
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How often it happens
Common red flags of a cheating – and often narcissistic – partner include:
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Suddenly guarding their phone like it’s state-secret material
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New passwords, Face ID or lock screen settings that weren’t there before
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Phone always turned face-down, on silent or in another room
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New “work drinks” or late nights that never used to exist
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Snapping or deflecting when you ask basic questions
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Changes in intimacy – from cold withdrawal to intense overcompensating
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Gaslighting: “You’re imagining things”, “You’re obsessed”, “You’re controlling”
Example:
“Every Thursday he says he’s at ‘networking drinks’. There are no photos, no tags, and he can never tell me who was there. When I ask, he gets angry and says I’m paranoid.”
Those details aren’t you being dramatic. They’re patterns, and that’s exactly what investigators watch for.
4. How Phones, Multiple Numbers and Apps Make Cheating Easier
These days, you don’t always find a literal burner phone hidden in the car. Technology has made it simple to run multiple lives from one device, and narcissistic cheaters love that.
Someone can now:
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Run several numbers on a single phone
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eSIMs, VoIP numbers and app-based lines
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“Work” numbers that magically turn into “private” lines after hours
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Use separate contact lists so certain names never appear in the main phonebook
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Keep entire relationships inside encrypted chat apps:
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WhatsApp, Signal, Telegram
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Instagram and Facebook DMs
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Messaging inside games or productivity apps
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Turn on disappearing messages, secret chats and auto-delete features
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Hide photos, videos and documents in locked folders or disguised apps
For a person with narcissistic traits, this setup is ideal. It allows them to:
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Feel entitled to do whatever they want
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Assume they’re smarter than everyone and “too clever” to be caught
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Maintain the main relationship at home while juggling extra supply on the side
Because of this, a whole industry has sprung up around multiple numbers, privacy tools and “discreet communication”. There is serious money in making it easier to hide.
New Tools Cheaters Use (and What PIs Watch For)
Modern cheaters, especially manipulative ones, tend to exploit:
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Burner apps and extra numbers used only for specific people
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Private browsers and incognito mode to hide searches and logins
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Photo vault apps disguised as calculators or tools
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Multiple social media accounts:
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One respectable, public profile for family and work
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One “real” profile for flirting, hookup culture and secret contacts
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AI tools that:
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Help clean up message histories at speed
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Generate fake “proof” of where they were
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Draft charming or emotionally tuned responses with minimal effort
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You don’t need to become a digital forensics expert. Even so, it’s worth mentioning to your PI if you’ve noticed:
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A “business” number or profile that seems to live its own separate life
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Random numbers showing up in screenshots or profiles
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Apps you never see them openly use, but they always protect fiercely
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Chats you glimpsed once and then never found again
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Heavy use of lock apps, hidden folders or “privacy” features
Investigators who understand narcissistic cheating behaviour know how these tools fit into a double life. They’ll factor this into their plan from the start.
5. Times, Places and Patterns to Watch
Surveillance is usually the most expensive part of an infidelity investigation. You don’t want someone sitting in a car for ten hours on the off-chance something happens.
Instead, you want to help your PI target the windows of time when shady behaviour is most likely.
Consider:
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When your gut screams the loudest:
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Are certain days always “busy”?
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Are there regular gym nights, “meetings” or gaming sessions that don’t quite add up?
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Where they might be going:
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Repeat suburbs, hotels, bars, gyms or friends’ houses
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What events are coming up:
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Work conferences
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“Boys’ weekends” or “girls’ trips”
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Christmas parties and end-of-year functions
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Example:
“He’s consistently unavailable between 6–9pm on Tuesdays and Thursdays. He claims he’s at the gym, but the gym closes at 8pm. The Uber charges to other suburbs always appear on those nights.”
With this kind of information, the PI can plan surveillance around high-probability times rather than guessing.
6. Evidence You Already Have (Even If It Looks Small)
You might already be sitting on a pile of useful clues without realising it. On their own they might look minor, but together they tell a story.
Legally and ethically, you can gather:
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Screenshots of:
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Flirty or intimate messages
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Late-night chats that cross boundaries
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Suspicious social media comments and reactions
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Call logs showing:
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Frequent calls or texts from unknown or hidden numbers
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Bank and credit card records:
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Hotels, restaurants, bar tabs, gifts, lingerie, flowers
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Photos of:
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Receipts or bookings you’ve stumbled across
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Items that appear or disappear with no explanation
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A simple timeline:
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Dates, times and brief notes such as “Said he was at X, but bank charge shows Y”
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Example:
“I’ve got three months of bank statements with hotel charges in the city on nights he claimed to be staying at his brother’s, plus screenshots of late-night messages with a woman from work.”
An experienced investigator can often pull clear patterns from what you’ve been trying to piece together in your head.
7. Be Clear About Your Goal (And Your Limits)
Not everyone wants the same outcome from a cheating investigation. In fact, being vague here only makes the process harder for you.
Some people want:
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Concrete evidence for legal reasons – divorce, custody, property settlement
Others are mainly seeking:
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Emotional closure – a clear answer so they can stop obsessing and move forward
And quite a few secretly hope:
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That nothing is happening and they can relax
Because of that, it’s important to be upfront with your PI about:
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What a “successful result” looks like to you
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Whether you plan to use evidence in court
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How much detail you’re okay with seeing – not everyone wants explicit photos or video
Examples:
“If he is cheating, I’ll need evidence to support separation and financial decisions.”
“I’m not going to court. I just want to know the truth so I can decide whether to stay or leave.”
The investigator can then shape their strategy – and how they present the findings – around your needs.
8. Budget, Boundaries and What’s Off-Limits
Private investigations aren’t cheap. Time, travel, equipment and reporting all cost money, so it’s better to be realistic rather than shy.
Have an honest conversation about:
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What you can afford overall or per week
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Whether you want:
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A focused operation around a specific event, or
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Monitoring over a longer period
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Where your hard boundaries are:
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No following or photographing your children
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No contact with your employer or family
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No graphic content if that would be traumatising for you
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A professional PI will help you prioritise and say, “Here’s what we can realistically achieve within that budget, and here’s when it’s most effective to act.”
9. Legal and Ethical Boundaries (So It Doesn’t Backfire)
A proper private investigator must stay inside the law. That protects you as much as it protects them.
A reputable PI will not:
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Hack phones, emails or social media accounts
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Install illegal spyware or tracking devices
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Break into property, vehicles or devices
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Pretend to be police or a government authority
Any offer along those lines is a major red flag. Remember, narcissistic people are experts at flipping the script. The last thing you need is your ex waving evidence of your illegal behaviour in front of a judge.
To protect yourself, ask the PI directly:
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What methods they use in infidelity investigations
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What is legal in your state or country
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How often their evidence ends up being used successfully in court
That way, you end up with clean, solid evidence instead of a legal mess.
10. Protecting Your Privacy and Safety
You’re not only exposing your partner’s secrets; you’re handing over very personal information about yourself too. Because of that, privacy and safety matter.
Before signing anything, ask:
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Do you have a written confidentiality policy?
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How will my data and documents be stored, and for how long?
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Can my case be labelled under a code name instead of my full legal name?
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Who in your office has access to my file?
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What happens to the evidence once the case is finished?
If your partner has been abusive, controlling or vindictive, say so. A good PI will adjust how they contact you, what they put in writing and how they manage sensitive material so you’re not left exposed.
Quick Prep Checklist for Your First Meeting with a PI
You can copy this straight into your notes app and tick things off:
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Partner’s full name, date of birth, mobile and email
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Home and work addresses, plus usual work hours or roster
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Vehicle details (make, model, colour and rego)
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Short summary of your relationship and living situation
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Clear list of suspicious behaviours with dates/times where possible
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Screenshots, bank records or other “receipts” you already have
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Notes about weird phone/app behaviour, multiple numbers or secret chats
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Your main goal: legal evidence, emotional closure, or both
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A realistic budget and any non-negotiable boundaries
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Questions about privacy, data storage and legal limits
Final Thoughts: Clarity Is Powerful (And Narcissists Hate It)
Hiring a private investigator to catch a cheating partner is a big step. Most people don’t do it lightly.
Even so, there are some hard truths:
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Living in constant doubt destroys your self-worth
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Being lied to and gaslit trains you not to trust your own mind
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Narcissistic behaviour is designed to keep you confused and off-balance
Evidence cuts through that fog.
Once the investigation is done – whether it confirms infidelity or clears your partner – you get one crucial thing back: your reality.
From that point on, you get to decide:
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Do I stay, or do I leave?
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What boundaries do I set from here?
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What support do I need – emotionally, legally, financially – to move forward?
At TheNarcSlayer.com, the bottom line is simple:
You deserve truth. You deserve safety. You deserve a life where you’re not constantly questioning your sanity because someone else is lying to your face.
If you decide to go down the PI path, go in prepared, informed and clear about your goals. Whatever the outcome, let it be the beginning of backing yourself – not doubting yourself.