I would have to agree with GravitonSurge on this one.
People hardly ever change. I think you should have made her try harder to get back with you. If she tried for a week to get back with you i would consider that a good sign that she has change or is trying to change. What are you going to do about Sean I mean i would be pissed off if one of my friends would date my girl friend two hours after they broke up with me.