Ok this is a slightly different scanerio
But i fell out with a friend who was a wg collage as well as a friend. (She hit the drugs heavily) She turned up at my house, threatened to out me to my family (my dad had just had a heart attack and she knew this ans she replied if he dies it's my fault! Thats how nasty she was)
She also threatened to send letters, profile details to all my neighbours outing me!
I told her i was calling the police, she said go ahead! So i did!
They were great, straight away had a pin notice issued against her. I also approached my solicitor and he sent a letter (cost me ?30), telling her that if she contacted me again we be taking her to court and getting an injunction against her and that she would have to pay my legals costs, compensation for the stress caused etc.
Funny enough i never heard from her again!
Ok i know this is different situation but maybe you should contact the police, get legal advice as the twat will prob shit himself and back off as soon as he knows could in trouble with the police/ law.