Title says it all really, ive known this girl for about 2 years, we classed ourselves as freinds, she's been in a long distance relationship for all that time and about 4 months ago we started fucking, she's just been dumped by her long distance bf 4 days ago, and told me today she's thinking about getting back with her ex.

I'm not going to lie to you guys but for some reason I'm feeling angry and bitter towards her and I can't get this out of my mind.

How do I deal with this?