I can understand why you would have a bit of resentment. The push/pull that she created made it difficult for you to break away.

As far as why she did this, she may not even know why she acted in such a fashion. She may have been more resentful of herself for not being able to break it off. She may have known it was best but not been able to help herself.

I would try to forgive and get on with my life. I know that at some point she cared deeply for you and I feel that even with her being nonchalant that she still does but knows it's time to move on.

I'm glad that you are able to move on with your life. It has been on hold for too long. Hang in there you are doing great!