@casual12,
Oh gosh.
I don't think you're a cheat, no. I think you drank too much and wound up in a bad situation. Men can be sexually assaulted too.
For the leaving you part, I just don't know. I want to say "no" because you're obviously having a hard time and I'd like to reassure you. But of course that carries implications and I absolutely want to avoid any hint of "your girlfriend
should forgive you." Lots of reasons, but they include 1) who knows, maybe she won't, and I don't want to give you false reassurances, 2) I think your best approach is one of humility and hope, rather than thinking that she should forgive you and there's something wrong with her if she doesn't, 3) it's not something I've ever really dealt with, so I don't know. I was cheated upon but it was a clear-cut case that ended up in a breakup. I'm pretty sure I wouldn't have
blamed my boyfriend at the time if he had found himself in your situation, but at the same time I might have had a hard time with the idea that he'd had some sort of sexual contact with another woman, and that he's not even sure what the contact was.
Hey that brings me to another thought, have you had any testing done for STD's since this happened? Do you think the worst-case scenario was a handjob?