why can't I just leave

My boyfriend and I have been together for one year and 4 months . And he went to his  lesbian friends birthday party . He got really drunk and she gave him hickies on his chest  bc they were playing truth or dare. When I saw them. I was about to cry, and then he told me what happen I'm still grossed out with what happened like I don't want to have sex with him or anything I don't even want to kiss him , but for some reason I can't break up with him , and it's not bc I think I won't find anyone else bc they're has been a lot of cute guys who try talking to me .idk what it is , I'm i to deep in love with him?