It sounds like he is bad news....You are no longer together for a reason, and regardless of if he has changed or not, burnt bridges aren't easily rebuilt. You were drunk and vulnerable, something it sounds like you allowed to happen. And then he blames you at how it turns out...and you sound like you're starting to believe it.
While you did make a few bad decisions, the whole blame is not your fault. You need to decide what you really want. Go deep within yourself, do you want the man you are engaged to, or the ex? It is not fair to you or your fiance if you still love your ex in such a way. It will only cause problems between the two of you.
It is ok to make mistakes as well

We just have to make sure that we learn from our mistakes, so as not to repeat them!
