I just want to preface this that I am completely against cheating in any shape or form. My best friend was in a very similar situation, right down to the drunken hook up followed by being sober and saying they wanted to do it again. There were other tidbits to his story that are probably different than yours. But I almost ended this friendship over what he was doing. I posted about it a month or so ago, so you can look up the threads if you're interested.

She needs to make a decision. She either wants to be with her boyfriend or she wants to be with you. Unless her and her boyfriend are both okay with an open relationship, then the two of you need to stop acting like a couple. Personally, I think you should cut contact until she figures out what she wants. It's not helping you any to be playing around with something you can't have. And besides, if she's willing to cheat on her boyfriend, and you two were to get together, who's to say she wouldn't just turn around and cheat on you?

I'm sorry if I'm being harsh, but I got a little triggered when you used the exact same words my friend did. To me, cheating shows a type of character I don't want to be friends with -- complete disrespect for others, selfishness, among other things.

Btw, things did end up getting straightened out with my friend. We're still friends, he learned his lesson, but definitely not as close as we used to be. Cheating hurts more than those in the relationship.