Ex-boyfriend? If you want this to stop, you gotta start camping at night by your car with a shotgun. Police will not do anything, even if they had him.
I'm really sorry that you are having to go through this. Suggestion: Try installing cameras inside the vehicle and near the tires. And set a bait: hire someone (with security background) to sit and wait inside the vehicle and apprehend the perpetrator. It's not ideal but it'll curb the problem. Getting the cops on board is even better. Good luck getting rid of this nuisance of a person.