Can't move on from relationship

I was married for 7 years. The relationship got very emotionally abusive and she is a pathological liar....lies about EVERYTHING!!!
We have 2 great kids somehow and it really depresses me that the family is broken up because of all this.
I can't move on....once I broke it off with her I thought I would be happy. I guess deep down I thought it would shock her into changing her ways...it isn't that I didn't love her, it is that she was killing me. The deception and name calling was too much.
Even after all that, I just can't feel that connection with anyone. I can't even have good sex with anyone. Sometimes I think if I just had a good sex buddy I could move past her...but since we broke up my libido is shot. I used to want sex all the time-with her. I can't seem to even want someone else sexually.
To make matters worse...she has moved on and is sleeping around town. She is self destructing her life...but still has been able to move on.
I don't know what it wrong with me. Why can't I be indifferent toward her and just forget she exists? Why can't I get over her? She was no good for me and I know that...so why can't I?