Especially difficult situation with an ex-husband...?

That's a tough sitch but you don't want to miss your son's marriage. Hopefully your paths won't cross. If they do just give him the stink eye and keep stepping. You're under no obligation to play "nicey nice" with your ex. Good luck & try hard to think of this moron as little as possible. He's cost you enough. Cut the mental bait & take back your personal power.