Street,
I think SwingFox is right and let it go. I would normally tell you to do what makes you happy. In this case you should hold out. Let her think what she wants because she is the one that left you. Always remember that you have feelings too and that she did not take them into consideration when she started seeing this other person. I would tell you to move on, but we are kind of in the same boat. Remember that she left u and you owe her nothing. I hope this helps because I know no one can take the pain away but time. One more thing, I believe in charma (what you do to others will come back to haunt you) so let time have it's way with her.
Good luck,
Hubman