Should I tell his fiance he cheated

[Hopelessnaive]

I met a guy at work a little over 18 months ago. We became friends straight away, within 2 months it turned to more than friendship. We talked all day everyday, spent every minute we could with each other. I really fell for him. He always said he wasn't looking for anything serious at the moment and didn't want anyone at work to find out as it would make things awkward for both of us. I never pushed him, but I hoped that one day he would change his mind. I knew he was the one I wanted to be with.

Only it turns out I was a complete idiot. Not only does he have a long term girlfriend (around 10 year relationship) but they've also recently got engaged. No wonder he wasn't looking for anything serious.

I am absolutely devastated. Ive barely stopped crying since I found out. He's now ghosting me as he knows I know. Im not even worthy of an apology or an explanation. I obviously never meant anything to him.

He doesn't use any kind of social media, or I'm sure I'd have found out sooner. But I've found out who his fiance is through other colleagues, and after a little searching I've found her on Instagram, so I could send her a message. I just don't know what to do. Do I send her a message and tell her he's been cheating on her for over a year, or do I just let it go and say nothing and try to forget him?
Part of me is angry and wants to spoil his relationship to hurt him. Part of me thinks she deserves to know, especially before marrying him, and part of me thinks I'd just get turned into the bad guy and maybe she'd forgive him.

YABU- don't message her.
YANBU- message her and tell her everything

I would tell her. Be prepared for her to either not believe you or blame you. She can do what she wants with that information. If you have evidence which I'm sure you will if it's been going on so long, then show that too. I would want to know, I've been there x

Going against the grain here.
I probably wouldn’t tell her. She’s nothing to you, and whilst I do believe in sisterhood - not at your own expense. You’ve said he’s senior and well connected at work. If you tell her, work life is going to become very difficult, it’ll be spun such that you’ll be made out to be crazy, and you risk your reputation.

It’s easy for people on MN to say tell her, but remember nobody here has to deal with the fall out of that.
My revenge to him would be telling him I’m going to expose him, but not tell him how or when. Just let him feel uncomfortable and live on edge, with no real intention to do so.

The are all good reasons to tell his fiancee. She might not appreciate being told but you can’t know that without telling her.

Once you are secure in a new job, I think you should also tell senior staff at the company he works for. At the very least he should be monitored when he is assigned less experienced staff to mentor.

I never understand people who say stay out of stuff like this. I would absolutely want to know if I'd been cheated on so as not to waste any more of my time.

Obviously evidence is helpful but even a random message from a random woman is usually enough to plant a seed of doubt and get the cheated on partner looking for evidence, ie checking cheaters phone etc.

Us women aren't stupid, we know there's usually no smoke without fire when it comes to stuff like this.

I understand that people are saying that you are only doing it out of revenge... but, she really needs to know.

Otherwise this woman is going to be on mumsnet in 5 years time after 2 kids wondering what to do about her cheating husband. And everyone will be telling her to leave him.

I am so sorry OP for what has happened to you. It sounds like it would be better for you to start looking for a new job. I'm sorry it's come to that. What an awful prick he is.

Am I right that you had been having sex with him on and off for over a year but always in hotels not at either of your places?

Anyway, I do agree his fiancée should be told.

People will tell you to stay out of it but if it were me I would want to know.

@PurpleFlower1983 There’s a difference between wanting to know if you were the fiancé, and being the person who’d lose a heck of a lot in doing so. I think that’s the piece people are missing here.

Blowing up his marriage, has implications on OP’s career and reputation. She doesn’t owe the Fiancé this in these circumstances.
We see it all the time, OP will lose lots and the cheating bastard will get another chance with his fiancé and be protected by his employer.

Oh I get all that, and if I were OP I would try and tell her in a way that didn’t come back on me, but it’s shit that the poor woman may end up marrying him potentially completely in the dark.

Yes I would tell her.
Not for revenge. But because she may have that sinking feeling that somethings not right already. She might have asked him if she’s enough, is there anyone else, checking his phone, wondering why he’s acting differently…. You know what I’m saying… she deserves truth, it might be that she is suspicious and he’s proposed to keep her happy. How awful to marry under such circumstances.

Look.

You just want to cause hurt, and I totally get that. But she does need to know, so you need to get the information over in a a really non hurtful way.

You'll get the end result you want, and you'll be a lot more believable. Because he's going to instantly paint you as the nutcase from work who he's had to let go etc etc.

Get your new job lined up, because you realistically can't stay there. The day after you leave, message her to say you're so sorry, and also feel betrayed, you had no idea and wanted to her to know because if he's cheating on the both of you, there may be others and you would never knowingly engage in a sexual relationship with someone who was actively sleeping with other people, and here are the messages to prove what you're saying. It's all about the messages by the way. He can't get out of those.

Then move on. Let her decide what she wants to do. She night want to stay with him, lots of women stay with cheaters. But you've done your part and then left the dirty git where he belongs. In your past.

Have you always hooked up in hotels? Are you sure you didn’t think he had someone?

If she just vaguely threatens exposure with no action he’ll just find a way to bully her out of the workplace.

Tell her OP - she deserves to know. You'll probably be painted as the bad guy. It's depressing the number of people who say keep your head down you'll only get grief from it. What about doing the right thing?

part of me thinks I'd just get turned into the bad guy and maybe she'd forgive him.
probably, but that doesnt effect you

tell her. Send the dates. Have you photos of you together at these pkaces? Yoy didnt mention photos, which is weird in a year ling relationship.

Also FWIW I have received a message like that in the past - although she knew, she was just mad he never broke up - and no, you won’t be painted as the bad guy if you were truly in the dark.

If you both knew then you’re both the bad guy. But I’m still glad I got that message.

Given you've got evidence, I would want to know if I were the fiancée so I could make my own decision on what to do with the rest of my life.

Personally I wouldn't marry him, but I'd probably also hate you. Not so much for sleeping with my fiancé unknowingly but because you were the catalyst for a big upset in my life. So just be prepared for that if you decide to tell her. And I have friends who were told something like this and decided to forgive the man, so also be prepared to find out he's still getting what he wanted.

The poor woman. I hope she finds out before she has kids with him. As it could be even more devastating in future.

You say he was your mentor at work. It sounds like he could have groomed you and an abuse of his position. You might want to consider a complaint to HR.

Rightly or wrongly, I’d tell her. Just be factual about it. And send evidence of messages etc. But as a pp mentioned, I can’t work out how you navigated weekends, Christmas, birthdays etc without realising he had a partner?

We talked all day everyday, spent every minute we could with each other. I really fell for him.

if this was a work colleague what do you mean by "we spent every minute we could with each other"? if you mean this was all conducted just in work time, then how does that equate to an affair. I think you've allowed your vivid imagination to get the better of you.

definitely don't make a fool out of yourself and contact his fiancée. How does you have her contact details anyway?

this plot has a lot of leaky holes in it.

Exactly, none of what's been said makes any sense.

She's said she has evidence of hotels they stayed in, dates they were together etc.

Try reading all of OPs posts before picking holes in her story to discredit her for no reason.

It was 18 months, so only one or two of those big occasions you mention. And new relationships don't often spend Christmas day together, even in long term relationships people are allowed weekends to themselves.

I think what you mean is "I wonder how he navigated these things while juggling more than one relationship"?

Years ago I had a similar situation then found out someone I thought was his friend had become his gf. (He said she was his friend) I never said anything. She found out anyway. She hated me and married him. I would tread very carefully you still have to see him at work.

'He always said he wasn't looking for anything serious at the moment and didn't want anyone at work to find out as it would make things awkward for both of us.'
Based on your own words you were obviously more invested in this 'friendship' than he was from the outset.
Forget him, move on and get on with your own life - if you tell his fiancee you will be cast as a shit-stirrer, troublemaker, jealous OW - this list is endless........
It is a shame that none of the other work colleagues thought to tip you off - perhaps he has past history of this behaviour.