How to deal with your boyfriend's jealous girl friend?

My boyfriend has a girl friend who is really jealous of our relationship. She'll make fun of me behind my back, has made up rumors about me, and is basically trying to convince and manipulate him into no longer being with me. Moreover, even when we did take a break for a while but were still friends and still talking, her abuse continued. It seems she won't even let me be friends with him!

I'm at a loss of what to do. He's defensive of her because they've known each other for a long time (however, he does not consider her a very close friend), and I think he pities her because of some things that have happened in her life. I've tried talking to talk to her about it, but she wouldn't talk to me in person. She at first sent me a message saying "I really think you're a great person and want the 3 of us to be friends" but the next day completely flipped and changed her mind. All I had done was seen her in person and asked if we could set up a time to talk together and she later facebook messaged me accusing me of "confronting" her and saying she "doesn't want to talk to me or think about it or deal with this ever again" and that "she was done with this when we broke up". She then said she would "continue to smile at me and say hi" but is "closed to anything further". To me, this seems like classic manipulative behavior, not to mention it proves how fake her claims she would like to make things better between us were.

I don't know what to do! This is causing a huge strain on my relationship with my boyfriend