Legal Question in Family Law in Texas

Go talk to the Justice of the Peace about evicting him. He is what's called a "tenant at sufferance."

If the JP folks can't figure out what to do, you'll need a lawyer.

There is a simpler solution, though: If you have any large, ugly, objectionable relatives, move them into your apartment. Make sure it's somebody who can be there all day and all night. Eventually, your ex will want to leave.