Reading your comments and the story, I think you sound like you are in a much better place than she is. I mean, you would think that the person who cheated, is the one who already has one foot out the door to something bigger and better. But she doesn't.
If I'm going to use my super psychic powers, I'll say that she has been unhappy for a while, and is still unhappy. This affair provided some excitement, but definitely didn't make her happy. Now she realises that the risk was not worth it, and things are worse than they have ever been, and this is definitely not making her more happy.
She realises that, while you are incredibly hurt, you'll move on quicker than she will, and you'll bounce back faster, because you have more going on in your life in the first place. She won't bounce back fast, because she wasn't happy or well adjusted to begin with.
She needed counselling like two years ago, to stop things getting as bad as they are. To face up to it and admit she has a problem.