Don’t go full bpd, you’ve got a good thing going right now, where your ex/friend think they’re better off than you at the moment but the truth is they’re headed over a cliff.

I don’t like encouraging hatred but the moral high ground is overrated here and you need some short term wins too. You can be ice cold toward people who are in the wrong, as long as you let your anger simmer (not boil). Respond to him when you have to, but say as little as possible and never initiate. Subtly communicate that you don’t even respect him enough to ignore him. When you notice he’s a bit uneasy or trying too hard around you that’s when you know it’s working.