Your Call (Oooh, This Is a Good One!): Should I Tell Her He’s Cheating on Her?


We get a lot of advice questions coming in at EMandLO.com, but sadly, we just can’t answer them all. Which is why, once a week, we turn to you to decide how best to advise a reader. Make your call on the letter below by leaving your advice in the comments section. 

Dear Em & Lo,

I’m having a moral crisis.  I met someone on craigslist a few months ago.  The nature of the relationship was that we both wanted a FWB situation.  The sex was fantastic!  I eventually got curious about this man, looked him up, and discovered he had a girlfriend.  I promptly ended our lusty relationship (my sister’s boyfriend cheated on her – she was devastated).  Now all I can think about is telling the girlfriend what a cheating d-bag her boyfriend is.  My rationale: I would want to know if it were me!  Should I do this?  Or stay out of it?

— The Messenger

What should The Messenger do? Let her know in the comments below. 



  1. Oh, please, please, PLEASE tell her! I was with a cheating liar who also stole from all of his exes. He smugly introduced me to a bunch of them at a nightclub. They could have aporoached me in the ladies restroom to tell me what a liar and a cad he was but they didn’t. He stole most of my belongings. I got together with 5 of them afterwards at the same time and asked them why they didn’t warn me. It turns out he had also stolen from all of them, and had also cheated on them, lied to them. That group of mealy mouthed cowards told me they felt they shouldn’t get involved and they felt it was “the Christian thing to do to forgive him”. Well what about me, his next victim?! Shame on those women! Anyone who knows someone who is doing something wrong, aware that he’s pretending he’s going to marry a woman so he can steal tens of thousands of dollars worth of her things – or if he’s cheating on her and can give her a disease – needs to lets his girlfriend or fiance’ know. If she stupidly decides to marry him after she’s been warned then the fault is all on her head. The person who warned her is no longer accountable for withholding such knowledge. Please don’t listen to these people who tell you to keep his girlfriend from knowing. She might not know he’s doing this and will dump him as soon as she finds out and he’ll deserve it. It might teach him a valuable lesson. People need to learn that fidelity and honesty is important in a relationship.

  2. Relationships are complicated and you don’t know if she knows but doesn’t care, or chooses to turn a blind eye for whatever reason, etc. Just because you wld want to know doesn’t mean that she does.
    I’m sure she’s aware of it, on some level, at least. Regardless, their relationship is none of your business.

  3. I understand where you’re coming from. I’ve been cheated on before. The reality is, he’s going to get caught, he’s going to slip up in a lie eventually. Do not take the heat or personal responsibility to do that. It will do you, him, or her no good long or short run. It’s not your call, because you may not know their situation to begin with. They may actually be friends or in a type of relationship that allows flexibility. Don’t get caught up in it, and focus on moving to someone better.

  4. If the shoe were on the other foot! If my gal was cheating on me, I WOULD want to know. I would not want to know who he was, but I would want to know.

  5. I am in a serious relationship, and I have to say I would appreciate the woman telling me if my boyfriend was cheating on me.
    We need to stick together and stand by each other. He made it your business when he chose to include you in his life when he was with someone else. All of this its too messy etc you don’t know her, well so what im pretty sure no one would want to waste their time with a cheating liar. Tell her so she can find a nice boyfriend.

    He is also putting her health at risk, if she is in a serious relationship she wont be getting checked regularly, he could catch something nasty and give it to her.

  6. I think you only have an obligation to expose someone if its an immediate family member such as a brother in law or something of that nature.. If its a friend.. Try to broach the subject with the friend. .then ask.. IF I KNEW SO AND SO was having an affair with someone else.. WOULD YOU WANT ME TO TELL YOU>? IF yes. .then say BRACE YOURSELF.. and do it.. Dont do it with everyone.. just very close people and know it may very well end your friendships… its so sensitive..

  7. Messenger, I am a crime show fanatic. I can tell you that NOTHING good comes out of a cheating situation. Since you don’t know the woman, I would NOT tell because it can backfire.

    You are going under the assumption that the woman will “thank you.” That is NOT necessarily the case. You have to understand that some women blame the other woman, even if it is the man’s fault. Some women do NOT want to know their men are cheating because it is easier to turn a blind eye. You have done your part by quitting the relationship, let Karma do the rest.

  8. You’re being selfish. You want him to feel the pain and embarrassment that you now feel from this incedent. You have no obligation to ruin a persons life because you are “pretending” to base it off of morals. You’re not the relationship police because you were lied to. You are mad at him, you want to get back at him and you think this is the way to do it. Do you think his lady and you are going to hang out for drink and pick up guys after this? I’m telling you right now, I would NOT want to know if my woman is cheating on me. I get checked regularly and I would find out she was if I caught something. Stop thinking of yourselfs. Most of you that replied to the post are woman, but how many of you are in long term loving relationships? If you are, ask yourself “how would I feel if my spouse was cheating on me”? Now, do you really want to know? I trust my partner even though we have a long distance relationship. It gets really hard at times, but we’ve been happy in our relationship. I don’t want the happiness to disappear because someone else thought they knew what was in my best interest.

    Posted via iPhone. Please excuse typos.

    1. I think your just afraid to be alone. And to say that you wouldn’t want to know is pretty sad. Your better than that and deserves someone who loves you. Imagine so money knows, they don’t tell you, the affair goes on for awhile, than one day you come home and she says it’s over I’m moving out right now. That would hurt more in my opinion.

  9. I had a similar less serious experience with a one-night stand – total stranger, I looked him up on FB after when I wanted to show flatmates his pic, and discovered his girlfriend is totally adorable and always instagrams him with cute captions. Sucks. I never told her. If he’s emotionally cheating I can see the argument for it, but like many commenters before me, I agree that in reality it just doesn’t seem worth it if it’s just (safe) sex.


  10. As someone who may die from the cervical cancer my cheating exhusband gave me from one of his mistresses, you NEED to tell the wife.

    I highly doubt you are the first person he’s cheated on his wife with. While you have the benefit of being able to choose to use protection, married women in relationships they believe to be monogamous see no reason to use protection as they believe there is nothing to be exposed.

    My exhusband was tested for everything before we got married, he was my first sexual partner and I discovered the hard way that he was cheating on me when it was discovered I had cervical cancer from HPV he picked up from one of his many mistresses and manstresses he was having unprotected sex with.

    I had no idea, and now I could die as a result.

    Yes she may go crazy at you, and she may not be grateful, but from one human being to another, you owe her the truth to save her life.

  11. I don’t know that you’re obligated to tell her, but I think you’re absolutely right to think that you’d want to know if you were her. I feel exactly the same way. I’d want to be told, no matter what, or even how. At the same time, I’m hoping it is eating him alive inside, so even if you don’t tell her, he will still get his due. Assuming he has a conscience.

    The STD factor is a concern too, even if you didn’t give him anything, who knows how many other people he is sleeping with. So this actually is a matter of life and death for her.

    But honestly, make sure first that he doesn’t have any dirt on you to use as payback and better yet, he doesn’t know where you live. You didn’t do anything wrong, so you do not need to ruin your own life over this. Only do it if you’re certain you won’t get hurt.

  12. I think you should tell her. If you were her, wouldn’t you want to know? Yes, take reasonable personal safety measures (whatever that might mean for your specific situation), but let her know.

  13. ^ Thing is, following your advice, she’d only be anonymous to the duped woman, and maybe not for long. The guy would probably know exactly who blew the whistle on him. He might then enact some crazy retaliation. Or, he might snap under interrogation by his partner. Or, she might stalk out the details – I’ve noticed that pissed-off women are the strongest sleuths in the world.

    That’s why my REAL advice is to say nothing, for the same reasons you advise anonymity: staying the hell away from crazy.

  14. Even after reading all of these really thoughtful responses, I’m still in the “if you decide to tell her just for her own health’s sake, keep as far away from the crazy as you can by being anonymous”.

    I’m not sure why people so easily can urge “The Messenger” to get closely involved in a situation with someone she doesn’t know over having sex with someone she barely knows. She isn’t dropping “the corpse of her committed relationship on her porch”. Sounds like this guy has already turned the relationship into a walking-dead scenario.

    A note that said something like… “Hey, I met your boyfriend online. We had sex. When I found out he was cheating on you, I ended it. I’m telling you this because if I was in your place, I’d want to know so I didn’t end up with a disease or wasting my life on a man who was cheating on me. Sorry to be the bearer of bad news.”… is going to get the point across just fine. The Messenger doesn’t need to deal with it more than that. She did the right thing and ended it, but doesn’t have to open her life up to a potentially really nasty and messy situation involving a stranger’s life by telling the woman who she is.

  15. I was recently in the same situation, only the guy I was seeing for 4 months was married.
    I broke it off and told the wife. She didn’t want to know who he was sleeping with as long as he was leaving her alone.
    I suggest telling the Mrs, give her all the info and your contact info for when she has questions.

  16. Regarding the anonymous tipoff method: I am going to agree with Johnny and disagree with others. No matter how you tell them it’s going to hurt them.

    If you ran over her dog you wouldn’t drop the corpse on her porch, ring the doorbell, and run away. Not even (and maybe even especially) if running over the dog was a complete accident. Not even if it was the dog’s “fault” for running out before you could see him.

    Well. Neither should you drop the corpse of her committed relationship on her porch. And as in my analogy, “but it was his fault” doesn’t give you permission to ring the bell and run away.

    And I think that actually resolves my earlier qualms: if you’re willing to own your part in telling her then go for it. Otherwise it would be better if someone with integrity let her know her partner has none.


  17. My first reaction was, “you sought out a casual sexual relationship on craigslist, and now you’re actually surprised that there’s a shady side?”

    But maybe you’re unfamiliar with Craigslist hookup culture. Cheating, obese threesomes, and sexual predation are pretty much what the (hetero) Craigslist hookup board is for. Be thankful – it could have turned out way weirder. Consider this a lesson learned, and stick to proper dating sites from now on. The type where a guy has a face pic in the profile and the “single” box checked off.

  18. I still say don’t do it, but if you must,t show yourself. No anonymous tips. That’s the cruelest way you could do it. Put yourself in her shoes – imagine an anonymous tipster told you your guy was cheating. Imagine the insane confusion you’d experience if you were forced to believe either your man, or a nameless, faceless accuser with a damning tale.

  19. I…


    I think the best answer is “tell her if you’re really sure that’s what you want to do.” Otherwise I’m really, really not sure you should.

    I’ve now lived in the very progressive Pacific Northwest for more than half my life. My PNW half says what could possibly go wrong. If this were a Portlandia script she might even thank you and you’d become wry “comrade in arms” coffee companions. I mean, you didn’t know, she didn’t know, you’re both wronged parties with the same ex in common. So no problem there.

    The other half of my life, though, I lived in a healthy mix of Southern Appalachian culture — rural, urban, suburban, exurban. And in not a single one of those places would I ever recommend it. Not least because she probably, um, wouldn’t thank you. She might blame you (hey, knowingly or not you did have sex with her partner!) And in a lot of those areas there’s a sort of half self preservation half diplomacy tendency to overlook what you actually know is true… unless and until someone brings it up in a way you can’t overlook. At which point one becomes “honor bound” to pull the fire alarm.


    Stereotypes aside there are actually plenty of people in the South who’d be all Portlandia with you. And there are plenty of people in Portland who’d publish your name with your transgressions and a warning all over Facebook, Yelp, Linked-in, Reddit, and maybe even on a billboard on your way to work.

    Bottom line: if you’re equally comfortable with either praise or blame then go for it. If you’re expecting a medal there’s at best a 50/50 chance you’ll get one. If your conscience won’t let you remain silent then please don’t. If you just want revenge on the guy then… I dunno, I think revenge is a really lousy motive.

    Final point: Would anyone’s advice change if the roles were reversed? Would you feel comfortable recommending that a man tell another man his girlfriend has been cheating with him? If your answer were the same either way then congratulations, that would be a good call. If you not then your answer should probably be no.

    Great, tough question. Good luck with your decision. However you choose I hope it all goes well.


  20. Ack I didn’t even consider the health ethics aspect! I guess I just am more familiar with how damaging “the crazy” from situations like this can be than any health issues that have stemmed from them.

    M’s anonymity idea is a really good one.

  21. ew ew ew. You must feel so icky from this, I know I would.

    I would say that you have a responsibility to inform her, maybe because of emotional ethics but DEFINITELY because of health ethics. If she thinks he is monogamous and she’s not protecting herself, she could be in physical danger.

  22. I agree with M. Give her the information anonymously so you don’t get caught in the back lash or get blamed. She might just stay with him anyway but at least you tried.

  23. I am The Messenger. I asked him if they had an open relationship (I really really hoped this was true) – it is not. He is indeed cheating on her. I just think my duty is to inform her. If she doesn’t want to believe me the choice is hers.

  24. Tell her. Put together the information that you have (presumably his craigslist posting) and put it in her mailbox with a note saying if she wasn’t previously aware, you thought she had the right to know. I’d suggest not even leaving your name. Whether or how she wants to react is between her and her boyfriend.

    I’m with you; I would want to know.

  25. I’d stay out of it.

    Yes, he could be in a non-monogamous relationship. But not being honest about that sort of relationship with a regular sexual partner doesn’t really sit well with me. I’ll say it could be a possibility, but not a good one.

    Chances are, if he’s a lying cheater, then the woman he’s with is pretty firmly wrapped around his finger. Maybe she knows something is wrong, but is in denial about it. Maybe she’s completely oblivious but would justify his actions if confronted. Maybe she just wouldn’t believe you – “everyone is just out to get my man away from me.”

    The only way for a person to get out of a deceptive relationship is to come to the realization of how destructive it is on their own. Nothing anyone says really matters if someone is caught up with a manipulative liar.

    Stay away from the crazy. Far away.

    1. Right. Why limit yourself to the portions on a box. Truthfully cheating can be a passionate catalyst to solve whatever problems they would be having to be this insecure about the relationship. This is even more true when you’ve the man is amazing in bed ( I feel sorry for those lasting less than 5 minutes, you have my condolences, and my left overs (; … especially when it’s so easy, just look here ) and the sex becomes monotonous after doing all the same moves. Need to fix the underlying reasons nobodys talking about first.

      1. Just to be clear JacksonK, when you say “cheating” you mean agreed upon cheating, as in an open relationship, yes? The word “cheating” connotes lying and breaking the rules, i.e. basically the opposite of a responsible open relationship, which is all about communication and agreed upon boundaries. But if you actually mean cheating as in sneaking behind your partner’s back without their consent when they believe you’re in a monogamous relationship, then we have to call bullshit: Saying cheating like this can solve relationship problems is like saying let’s use MORE pesticides to try to fix the disappearing bee problem, or filling your cabinets with sweets just test the strength of your diet, or having a baby together to solve your relationship problems. Not a good idea.

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