I don't think she has done anything so unforgivable...it also sounds like you're only really punishing yourself by staying away from her because you genuinely miss her. Have you considered agreeing to date again provided that she cuts off contact with her male friend? Or asking her to cut down on contact and only talk to or see him when you're around, and there are a big group of people involved? I can see this from both sides, though...it is possible that she was or is cheating, but having been in her situation numerous times when I was younger and not as considerate, when a girl is sleeping with her male friend before she ends her primary relationship, she will almost always then openly be with the male friend afterwards. If she is wanting you back, there is a chance he is genuinely only a platonic friend and your jealousy and/or insecurity could be clouding your perception. You certainly wouldn't be the first BF to freak out over his GF having a guy friend and dumping her, then regretting it. I would suggest that you talk to her in a calm and mature way. I don't think you should try to dictate who she can and can't contact...I can see why you might be bothered, but ultimately you can't control her, and it's not really right to tell her who to be friends with. But if you do want to give it another shot, you need to have an open, honest conversation with her about trust and decide what it will take for you to trust each other this time around before you get involved with her again, if you want to go that way. Do you have any reason to think anything more than friendship has happened between your GF and the guy in question? If so, then I'd say move on, but otherwise, I certainly don't think she's necessarily someone you could never trust again and deserves another chance. Assuming she is faithful to you and you can trust her and respect her independence, I think you guys might have a shot...and I usually disagree with the people here who take an optimistic approach to advising people about getting back together with someone after they've broken up. In most cases, I think it's a waste of time to mourn an ex and hold out any hope whatsoever of getting back together, but of course there are always exceptions to any rule. Hopefully you'll know what the best choice here is for you and decide accordingly...good luck!