First off I would save EVERYTHING that he has written to you, or sent you. If he has called your work and told people that you are a whore and a user, I would get a restraining order aainst him. That is considered harassment, and you don't need it, and you don't deserve it. Call the cops! Show them the letters, have co-workers verify this guys is nuts.
Second of all i would change your cell number and your house number.
I would tell the receptionist or the person in charge of taking phone calls at your work to screen your calls and write down how many times he calls. He can be charged with stalking and harassment.
Last off, stay off the chat rooms. Chats are not the bestway to meet people, cause most people have their own little fansity life that they live off the internet, and when the truth comes out, things are not always fun.
Hope this helps you.
Amye
http://www.noir-ailes.com/amye