Step 1: Block on facebook.
Step 2: Make sure your friends know that you're not comfortable being around him/talking about him/whatever, and ask that they respect that. They can still be mutual friends with you and your ex, but they should listen to how you feel about it.
Step 3: Ignore your ex. You broke it off because he was insane, and this is pretty much just proving your point. Getting angry over it all is only going to give him the satisfaction of knowing he's getting his "revenge." If he has issues getting over you, let that be his problem. Move on, and don't get caught up in his drama.