Created a throwaway for this one... In these scenarios it is never a one answer solves all because it depends on a lot of factors whether or not your relationship can/should move forward, but all I can do is share my experience:
We met through a group of mutual friends. I became very good friends with them separately and hadn't met him since he lived 2 hrs away. I (25f) was dating him (25m) for almost 6 months LDR when I found out about his incident which had happened 4 months in. It happened while he was away on a business trip and it was with a friend from the group who I had never met that lived in the town he had travelled to.
The girl worked in a bar environment so the last night he was there they did a big night out on the town. I didn't hear from him, but it was early in our relationship and since I was friends with all of her mutual friends I never really expected them to do something so dumb. Anyway I wake up to a text from my sister about a weird fbook post. I go onto his page and am a little irritated, I see the girl had posted with his account a stupid status "I am (my bfs name) and I looooooooooooove (friends name)." It was posted at 3am. Drunk message obviously I text him a not cool and better take it down and move on. Still trying to remain calm I confronted him about it that weekend and he laughed it off.
Keep in mind we were long distance at this point so time moved a little faster bc our relationship was over the phone and on the weekends occasionally every other weekend. Things slowly started to get weird. I probably would have noticed sooner if we were in the same town/state, but unfortunately it took me two months. I finally snooped after he weirdly was strongly insisting that I moved in with him ASAP. I found texts b/w them basically her saying to forget about it- it never happened and then him continuously asking to talk to her to get advice about how to fix this with me bc he really wanted us to work. She just said tell her what happened - nothing (so basically continue lying) and then just stopped answering him. The last few messages were him basically giving up on getting her help ("hello?" "alright i guess ill stop asking" etc).
I try asking him about the trip casually and his response was to switch back to me moving in at which point we argued and I left. I waited a day to calm down and then dropped my knowledge on him and pushed for details. Unfortunately it took THREE days of me just yelling and breaking him down to get the truth. Each day I received a little more info. He was crying and begging- ugh it was a mess. He drove down and we went on a walk in the woods together to talk.
At this point I was ready to end it. I am a physical person. I love sex and can understand that if you put yourself in the wrong scenario (ex: very drunk and alone with someone attractive to you of the opposite sex) shit will happen. The trick is knowing not to put yourself in that scenario and knowing your limits. Also, I had been emotionally cheated on in my last relationship (almost 4yrs together). I value honesty above all after that experience since my ex over and over again lied about his feelings about us and our relationship. This was the first guy 2 years after that I had actually like and he was, as far as type goes, a totally new direction for me. I was crushed.
We went on the hike and at this point I was just defeated. In my mind it was done and this was just closure so it would not be awkward with my friends. Then I saw something I had never gotten in my last relationship. He was genuinely sorry, a complete wreck, and willing to do whatever it took to gain back my heart and trust. He also totally opened up to me and explained where he was at the time. Since this message is already a novel I will share what he did:
He had never been in a serious relationship before. The guy was 25 and the only thing he had in his past that came close was a girl he dated for 6 months in high school.
He had severe self esteem issues due to the fact that that one girl had cheated on him with his best friend and slept with the friend yet never did with him. He is a very intelligent guy and is the type that when he fails at something he internalizes it and obsesses over it.
He was totally freaked out by the thought of being serious with someone. He had no idea how to be open and intimitate and it scared the shit out of him. Being an only child did not help things much and while he is very charming and social he easily can just shut himself away from everyone else and be alone.
After a long conversation, I was more calm. Relieved to finally know it all, but still not even close to getting back together. He was ready to do whatever I needed to take him back. At this point I think that the fact that he was so willing to do what my ex would not - fight tooth and nail to get me back - that I said fuck it. He had to:
Accept that he was on probation- he had to remain faithful, but we were not really together at this point. We would both not date anyone else, but also take a break from seeing each other as often. We did every other weekend instead of every for example. Sometimes less depending on me.
go to therapy- It was obvious that he had self esteem and intimacy issues. Also, he was almost more of a wreck about the whole thing than I was. There was no way I could or would take care of him as far as that went and that he needed help. Therapy was a MUST.
*cut off contact from that girl- He needed to make it clear that while he would be civil in friend scenarios the fact that she participated and then refused to own up for her part in things was not cool. She just wasn't a good friend and turned out not to be a good person either. Not only did she have an affair with her bosses son right befor she hooked up w my bf, but she had also slept and cheated with most of the guys in our group of friends before she had moved out of state. Everyone was pretty much done with her crap. (Also side note - I sent her a very calm message explaining that I knew and I only held her 50% accountable since it takes two. That we were going to work to try to get through this and that I would appreciate her giving us space and respect. That I would not bad mouth her to any of our friends and if we ever ran into each other I would be civil, but that was all I could do.)
Get tested- for OBVIOUS reasons - turned out he had done that already at least.
Own up to our friends about it- There was no way in hell I was facing our friends and pretending we were fine. They needed to know what happened and with who and I would be damned if I was the one to tell them. I also did not want to have future awkwardness when she was around. I just needed people to know why I would avoid certain things and maybe not to sit me next to her at a wedding. I am not the type for cat fights she just needed to stay away from me.
Lastly he needed to realize that I was going to be hot and cold for a while. Somedays I might be a raging psychopath and others fine. He would just have to ride that out. If I needed to see something texts, emails, etc he would need to show me and NO DELETING messages. NOTE: Dont get his password its a slippery slope to insanity. Also, that physical intimacy might be hard for me at times. There were certain things I just flat out couldn't do for a few months after. Basically he would need to have some patience.
And he did it. He did it all. We had rough patches of course, but his going to therapy really opened him up and showed him how to be in a relationship where you are honest and you communicate. The best way to deal with the anger is to really find out what you NEED from him to get past it. Being open and honest and him doing the same is the only way you can get through. Now 2 and a half years later we look back at that whole time period as the unfortunate event that unexpectedly brought us closer together in the end. Not really a story we will tell the kids one day, but its the gods honest truth. I am not at all thankful for what happened, but I can't help the fact that that is the truth. We live together now and have a very normal healthy relationship. There has never been another questionable event and we love each other very much. I don't know what the future will hold, but I really do believe that in rare scenarios it is possible to move past these things as long as you do it together.
Best of luck to you and your bf going forward. I hope this all made sense and isnt too much of a wall of text. Writing is not my strength.