You have no choice but to move on. She has decided that her marriage and child are more important. A family often wins out over an affair and it should. Unfortunetaly alot of damage has already been done. Being friends really isn't an option because that will only get you in more trouble or make the situation harder.
You played a game you shouldn't be playing and you lost.
I think kvinneakt is right. Look at your relationship with your girlfriend. You have a choice to either put your focus on that or move on. It's not fair on her and I imagine you have been neglecting her. She doesn't deserve that.
Heidu

Every path to a new understanding begins in confusion- Mason Cooley