Should I tell his fiance he cheated

There’s power dynamics at play here, and not just between OP and her ex. That they shouldn’t exist doesn’t mean that they don’t, and as such OP needs to consider the very real consequences she could find herself facing.

‘Doing the right thing’ could cost OP not just her job, but her entire career.

Don’t act. It will not give you anything. Be the bigger one and find your own peace.

You could make it an HR thing, and she could find out that way. He was a mentor and in a position of power over you. He should never ever have used his position at work to get his end away. This smacks of all sorts of wrong and I doubt you’ll be the only one.

I was in the same situation once with a senior work colleague. I had absolutely no idea. We were engaged and going to sign a lease for a house together or so i thought. I told the fiancée. Her family then proceeded to hound me if they saw me when I was out (I didn't know who they were so I couldn't avoid them at first but they sure as hell knew who I was) and i ended up needing to move house. They still got married which is their deal but be careful if you do say anything. It might not go how you think.

This is so naive. Of course work will be an issue. Whose side do you think HR will take and whose career do you think will be blighted? I’ll give you a clue - he’ll emerge smelling of roses.

The fact that you've decided someone came on looking for advice about a situation they made up says everything about you and nothing about OP.

Who do you think you are barging in here with accusations and insults?

I sincerely hope with everything else she has going on that she doesn't waste her energy defending herself to you.

Remember, it’s not YOU hurting her by telling her. HE is the one who is hurting her. You’re just the messenger.

The fact this lowlife expects OP to stay silent is a big red flag. That's not on, he's controlling the narrative.

As regards what benefit it will give OP telling the truth. If, as I mentioned earlier, OP handles this with HR firstly and protects herself then work should not be the main issue. After that, she's simply telling the truth. Why does OP have to tie herself up in knots keeping her head down? What does that achieve?

OP still has to heal her heart, in her own way and I agree, revenge alone won't help. If this is more than revenge, if it's about saying what happened, holding her head high, then more power to OP and I think she'd be dead right.

I’ve been the cheated on wife. Transpired lots of people knew. While I sometimes wish people had told me, I also had a baby at the time and the cheating had occurred through our entire marriage so it was an absolute lie, all of it. You want revenge, I get it, but her whole life is going to explode in ways you can’t possibly imagine. I’m 11 years on and I don’t think I’ll ever quite get over that betrayal. It has changed me as a person. I have chosen to remain single as I don’t trust my own judgement any longer. So think carefully about wreaking havoc on her life. I am not for a moment saying he should get away with it, he shouldn’t, and eventually he will be found out. They always are. However, don’t do this out of
bitterness because it’s you swallowing the poison hoping somebody else will die.

If you feel you have to tell her I’d make a throwaway anon account and just say the bare minimum. He’s going to know it’s you. I’d also make sure I was in a new job. I’m sorry this happened to you. Some men are fucking foul.

How will she benefit? She’ll be worse off. If it was me I’d find a new job and walk away without a backward glance. Let karma take care of it.

I don't think you can win either way.

He abused his position.
He deceived you.

You're vulnerable at work - he could so easily turn this against you.

Tell her and he'll do the whole 'woman scorned' routine.

You can only put yourself first here. If you feel strongly about telling her, then be prepared to look for another job.

I expect she will find out soon enough - there will be someone else along the way.

If I were her, I’d definitely want to know.
Please tell her.
No need for any ‘attitude’ or sordid details - just the cold, bare facts.

OP was deceived. If her motive is revenge based on being deceived, why is that such a bad thing? The fall out isn't her responsibility.

Why are women not allowed to stand up for themselves?

Oh no! I did not rtft and didn't know he was a mentor. That puts a whole different slant on things. Instead of telling his fiancé op definitely needs to tell HR. Listen to @GrannyJJ whose advice is spot on. What a turd he is.

I would personally start looking for alternative employment. Although none of this is your fault and you shouldn't have to move, you are now stuck between a rock and a hard place. If you stay in your job and stay quiet, having to work alongside him after what has happened between you will be unbearable. Being heartbroken and being forced to see him every day along with hearing news about his upcoming wedding sounds horrific.

Objectively telling the partner being cheated on is the right thing to do and in most circumstances I would be advising this. However; this could have disastrous implications on your career and working environment. It isn't worth sabotaging your peace at your place of work where you spend a great proportion of your time.

There is a high likelihood that he will retaliate and seek revenge from you telling his partner; he could also frame you as a psycho trying to sabotage his relationship to other colleagues. You don't want your colleagues viewing you as a Baby Reindeer type character or maliciously trying to destroy a happy couple. It isn't worth risking your well-being, peace and reputation in this circumstance for the sake of seeking justice for a woman you have never met. Put yourself first, there almost certainly will be other women and she will find out about his true nature eventually.

If she hasn’t sussed after 10years that he is a piece of shit on her shoes then there isn’t any point telling her because she won’t believe you. OP you won’t have been the first, you probably won’t be the last.

What you need to do is look after yourself.

I would tell her. But I’d make sure I was doing it because she needs to know the truth about him before marrying him, not just to get revenge on him, no matter how tempting that would be. Also she needs to get herself STI tested. Bet this isn’t the first time he’s done something like this, he sounds pretty skilled at it.

Men like this leave such a trail of destruction behind them because their victims take on the shame of their actions. First I would protect myself by getting a new job. You need to do that, he will prevent you ever getting anywhere in your current place of work now, so accept that and move on. Once Id done that Id be making sure HR knew, maybe in an exist interview, how my older much more senior 'mentor' was behaving with junior employees.

Once Id left, I would also be sending a message with evidence to his fiancé. Saying to her that I was extremely upset I had been involved in a cheating situation I had no idea existed. And that I could not in good conscience say nothing.

Then I would move on without a a second thought or look back, knowing I had done what I thought was right. And hopefully contributed a little towards protecting others from this bell end, who thinks getting his dick wet is more important than hurting the people he supposedly cares about.

Yeah I agree, marriage is a big financial commitment. If she's got assets he may be marrying her for them, I've seen it happen within my partner's family. The cheating did stop once they were married, but I doubt she would have settled down with him if she knew he'd been shagging around.

Although if you know your ex is well off, and she isn't, maybe wait until they are married so she can take half his shit 😁

@Hopelessnaive so you’ve never been to his place and you’re concerned she’ll just forgive him. And maybe you just didn’t want to see it. I have to agree with @SquashedMallow, to be honest.

I would still tell her though because she deserves to know, if she doesn’t already. It’s too serious. Whether they work on it or not it’s their issue to sort.

He was your mentor? That’s inappropriate that he took advantage and HR would definitely want to know. They wouldn’t be interested if it was a normal colleague relationship that ended normally but this is abuse of his seniority and the fact he was making you stay quiet whilst he lied is something that I wouldn’t want in my company.. your career isn’t at risk if you do this properly. Tell HR and say you want it on record but no action - it’s just in case you face any issues.. then sleazy Joe might think it was someone in HR!

She is a complete stranger to you. I would leave well alone. This man tricked you. Your beef is with him, not her. Also, are you sure that he wasn't on a break with her when he hooked up with you? If this is his MO then he will be found out soon. Concentrate on trying to repair the damage he's done to you. Try to take care of yourself.

I’d also be tempted to mention this to HR - you went into a relationship with someone at work who you thought was single and it turns out he lied and isn’t and is now creating a difficult environment for you as it’s not a normal break up - he lied to you…. however he is senior and I’d want it on record in case he could be an arse to you. He’s likely to tell his buddies at work.. He’s proven himself to be a liar and a cheat and also cruel so these are not features of a decent manager. Then I’d message his fiancé anonymously to tell them factually that he’s been having an affair with someone at work. Protect yourself first. You had no idea he was lying to you and tbh you won’t be the first he’s done this to.. you’ve done nothing wrong apart from being naive. Yeah his fiancé will get hurt but that’s his doing. Better to be slapped with the truth than kissed with a lie. Write it as if you are a colleague of his. Don’t put yourself in the firing line. Then if he accuses you, you can go to hr and tell them he’s harassing you. But they will have the background info in advance. You cannot get sacked or into trouble for this. He’s played a game of fuck around and find out.. literally!!!

Is it possible to talk to someone at work who you trust? Someone who understands how HR roll in your organisation, what the culture is like.

I know this might impact any promotion going forward however I wouldn't be so sure that a big company like that will see him in a good light. Aside from that, it could spell trouble for them and they won't want that. I actually wouldn't worry about work so much but that's something only you can assess.

I personally would tell his girlfriend, with evidence if possible.

To those saying that she should say nothing. Why shouldn't she stand up for herself. He's behaved appallingly. Staying quite means he will do it again. F**k that, OP has every right to do what's right for her.