I'm not going to help my ex pay back our paypal credit debt
Won't that also hurt you financially?
I honestly don't care, as long as it hurt him.
I can understand you frustration with your ex-partner, but I you should not make them pay your debts, it is wrong. One should always honor their financial commitments, especially debts. You can get in serious trouble if you don't do that, even go to jail.
I don't think it's that serious. This is just a warning for him and if he doesn't leave me alone it's going to get much worse.
Being upset at him is fine but that still doesn't mean not paying a debt to punish him is a good idea. The consequences of being put into collections or worse just isn't worth the hassle if you're doing this just to teach him a lesson. You should always strive to pay back your share of the debt, both during and after a relationship ends.