Are there tips from psychology on getting over someone who caused you mental and emotional damage?

I feel like I'm suffering big time yet should be thinking good riddance! How to I convince myself that not being with someone who lied and cheated and left me for a girl who lied and cheated to be with him is for the best? How do I stop feeling like the loser he couldn't commit too, whilst hooking up with a girl who did so many horrible things to me in order to get my ex. I know I should think I am better off, I just don't feel it! I feel really envious of the girl who 'won' (her words) and cannot reason with my head! I really do know how I should think, but can't seem to believe it myself. Help?