My name is XXXXX XXXXX I'd be happy to answer your questions today. I'm sorry to hear about your situation.
You are not responsible for the criminal acts of someone who is stalking your girlfriend. Give the apartment copies of all police reports and the restraining order, to show that this person is not your guest or invitee (or your girlfriend's). It may also help if you give them his address, so they can sue him personally for the cost of repairing the damage to the premises.
The other option is to tell the girl you're dating that she cannot come to your place again until the situation with her ex is resolved. If you can show management that you have told her not to visit (since it's her presence, not yours that is the problem and she's not on the lease), that may help.
If they want to evict you, they have to go to court
. That means that you would have a trial
where they would have the burden of proving that it is your guest who is causing these problems. Again, the police reports and restraining order will help. Copies of any additional documentation that you can get from police will also help - including phone records showing how many times you've called the police on this guy. If you can establish that you have no control over this person, you're not liable for the damage he caused (and you could sue him for the value of the judgment if the judge did find that he was your guest).
It's surprising that police are essentially doing nothing. If you followed the person who vandalized your place and got his license plate number, that's pretty close to catching him in the act. You may want to talk to a superior officer about everything that has happened and ask why they're not doing anything. If the girl knows where this guy lives or works, police should be able to serve him with the restraining order - and since you have his license plate number, they should be able to find out where he lives.
If you have any questions or concerns about what I've written, please reply so that I may address them. It's important to me that you are 100% satisfied with the service I provide. Otherwise, please rate my service positively so that I get credit for answering your question. Thank you.