I am sorry you are going through this.

He seemed sincere all along but wasn't. Why would his apology be sincere? If it is sincere in any way, it is only in that he is sorry only for himself that you found out. Now you are feeding into his dysfunctional ego by contacting him. It's a selfish game for him and now he knows he still has you hooked. Unfortunately, there are many people (of both sexes) that are like that. It never ends well. And you can bet the story he is telling his fiance and family does not make you out as an unwitting, innocent party to this . . . he is doing a character assassination on you. Anything to make himself look like the victim in this.

Who cares if the man apologizes and is sincere? He is a man of zero integrity and you are by far the winner in this situation for kicking his butt to the curb. Be thankful you found out. Walk the eff away. Immediately.