Stick with the no contact. Even letting him know you found out about his behavior sucks you back into his world. He behaved horribly, but I assume you knew that which is why you divorced him. Even doing something as simple as letting him know he was an ***, will give him the message that he's welcome to wreak havoc in your life even though you're not together anymore.

Do not let him continue to control your life. His behavior is his own, it does not affect your life anymore (except where the kids are concerned). The way I see it you have two choices, let this blast from the past make you miserable or be grateful you got out of the marriage when you did.