Try getting her to forget him. I'd stay with her if I where you.
If it continues confront her and just let her go back.
I suggest banging her before it's too late.
NEVER BEG!!!! I like to become a little more distant, less in your face. Make it seem like you can live without them. Most start working to bring that "old you" back.
She is not over him. You will get hurt. I hope yo get out of that situation. It is great that she is being honest about what she feels but this does not end well. Don't get hurt.