He broke your deal and your trust. Even if you were to forgive him, it's up to him to make things right. This ball is not in your court. if he thinks things can just go on after this, then he doesn't understand the magnitude of his actions and he needs to. Thing is if you call it a deal breaker, then it's obviously a very high priority thing in your value system and will llikely not change. Not that it should. It's not up to you to violate your own value system for someone else. He needs to respect your values and show you that he does or you need to find someone that will or your relationship will probably remain rocky.

Thing is a guy that is so quick to jump into bed with another woman after a long term relationship that he claims to have loved his partner is to be questioned. He may change but unless you're pretty darn sure of it, I wouldn't put all my eggs in this basket. At this point I don't think he's trustworthy. his devotion to you has come into question when he is able to be intimate with another so fast. Sorry to tell you this but in my view this is just obvious.