At the very least, minimize your interaction with him. Make yourself as boring as possible when he is around you. If he could just lose interest in you, that would be the best outcome.

I agree with the poster above who said stop trying to reason with him. He is not open to being reasoned with. You can repeat certain things, like a broken record, but don't bother thinking that you are somehow going to get through to him. You're not.

Anything you do to give him some pleasant interaction is just reinforcing his belief that he wants to cling to you. Every time you consent to him being around you reinforces his belief that he has a right to be.

As we all should know by now, the police can not guarantee your safety. Still, I would fill out a police report for every single illegal violation of your space that he perpetrates. Someday, it might be useful.