What can I do legally about someone slandering me?

I broke up with my boyfriend of 2 years in January of 2008, since then I have had very little contact with him, but he has spent alot of time talking about me. On more than one occasion he has posted on the social website facebook, that I am HIV+ which I have had tests proving I am clean. Just today he emailed my brother's wife and informed her that I was HIV+ and to please notify my parents because they needed to know to take care of me. I have talked with my parents as well as the rest of my family to inform them that I am fine. If there is anyone that can please advise me on this, he has the entire town I grew up in believing that I am HIV+, someone please help I am very desperate for an answer. This individual has made my life a living nightmare since meeting him. I need help.