Step away from him... and by that I mean... stop reading the emails, stop calling him, debating with him... trying to figure him out, and what his next move might, or might not be...
It's NEVER going to lead you to a place of peace. Never.
As Anvil said, you have a separation agreement, he's obligated to pay... you don't owe him ANYTHING for that money. Do not feel like you have to play his reindeer games.