Should I stay or should I go?

Okay so there's this guy that I like(d) a lot. And I feel like I've known him for a while now, and we're REALLY close. Also, our relationship isn't purely platonic, but it's also much more than just a physical attraction thing. The reason we're not actually dating is I guess he's just not ready? Anyways, he came out of a serious relationship not too long ago, and it's almost been a year since him and the girl have been broken up. Two nights ago, he was talking to his ex, and went over to her house and, they did it. He's really sorry, and I guess he wasn't thinking with the head on his shoulders, but I still don't know what to do, I mean I can't say anything because we're not official, but then again he doesn't want to be.. so there's no promises that this won't happen again. Again, I really like this guy and don't want to lose him because I know it'll be hard, but if it has to be done, it will be. I'm wondering what everyone else's opinion is on what I should do? I'm not going to base my decision solely upon everyone's answers but I'd like to see what everyone else thinks.