Cliche saying...but if it didnt hurt so bad, it would never have felt so good.

I say withdrawl all attention from her. No sex, no contact, nothing.
You do not diserve to be a leftover, and that is how she is treating you. No one diserves that.

It will be hard, no doubt, but I say ditch her ....ignore her, never speak to her again. She is bad business.
Replace her with someone else to distract your mind. It may not ease the pain, but it may make you forget about it for a bit, as time goes on, you'll find yourself wondering why the hell you looked her way in the first place.

Good luck.