I broke up with my ex girlfriend about six weeks ago. It has been the fourth time I broke up with her, but we were dating for three years. Anyway, a month ago, she said she wasn't coming back. Now, I caught her sleeping with someone else already?

Can she possibly move on that fast? Three months ago, we were talking about getting married. I was the one who ruined the relationship, but I still treated good overall. Sex life was good. One month after we break up, she sleeping with someone else already?

Someone help?