Do you have proof he owes you thousands?

Lawyer up?

Hell, even a bluff on a lawyer will strict fear.

"I have been talking to my lawyer, and he believes it will be best if we settle this out of the courts, we both would end up spending more money on lawyers than what you actually owe me. So if you want to go to court over this, fine by mine, just know that you will have lawyer fees on top of what you owe me"

A friend of mine pulled that card and it worked surprisingly.

But really.... is that a reason to stick around in a shit relationship?