I'm not surprised. It's typically hard for a woman to deal with a guy that still has feelings for his x. Not that you did anything wrong here, you can't help who you care about. But on your current GF's side of this, I understand.
My husband and I are dating a girl, but I wouldn't even consider dating his x. Maybe that's just closed minded of me, but she doesn't do it for me at all. Not to mention the jealous factor of their past........