Ok this one is going to sound completely crazy but take my word for it. If you want her back...
Move on.
Once she sees that you aren't showing interest in her she may take a change and realize she misses your attention.
Right now she has everything in her hands. She has a guy she left you for, and then still has your attention. What good would it be to come back when she can already have her cake and eat it too?
Moving on is the toughest thing I could probably tell you to do but it works. Give yourself time to rediscover who you are as a person. In time you will gain motivation and security in yourself and when that happens you may look back and decide you don't even want her back anymore!
We all deserve to receive as much love as we give. Right now you are allowing for a one way relationship that caters only to her.
Best of luck
