Mate, you didnt do anything to "deserve" this. The fact of the matter is she didnt CARE enough about the relationship she was already in.
When the cats away the mice will play.
So dont let the door hit her in the ass on the way out. Kick her to the curb.
If shes changes her mind and tries to get back with you dont play the fool and let her come back. If shes done it to you once she WILL do it again. It would only be a matter of time before she,once again, left you for another guy.
Dont play the broken-hearted fool. Dont let this get to you. Feel better that it happened now instead of after a wedding. THAT would truly suck. Be glad it happened before you blew anymore money on her. Expensive jewelery or other gifts cant buy love. They just get someone to hang around for a while.
On an ironic note: you can rest assured that she will do the same thing to the new guy. Not that its a relief, but in a way I suppose it could be.
If you should see her, be nice, be polite, and be on the lookout for someone you CAN trust. Dont let her see you get upset or shes going to have a psycological victory. Show her youre made of steel and that she hasnt hurt you in any way (even if she really has) and that youre glad shes gone so now you know what you ARENT looking for.
Chalk this one up as an experience. By the time you go through a few more things like this youll have a much better idea of what you really DO want in life.
She AIN'T in the list