John is right John.
Just think. She thought om was all that. Most likely turns out he was just a man, no greener pasture. Gonna take her a while to get over it. I think my ex is going through the same thing. Unlike you I don't think I could handle it if she wanted back. Alot more happened with us.
Just be supportive and yourself.
Have the attitude of "hey, I could take it or leave it". It works. That drives most of em crazy that you are so apathetic.
Takes alot of practice.
Ron