There's no shame in not wanting him back. People change and so do their feelings. Perhaps there is someone better suited for you. 

I also went through the same thing - I worked so hard on my ex and tried to force it because I felt like I wanted him back (I was living in a state of desperation), but then another guy happened and I developed feelings for him (I will post my success story soon, as requested by Lanie). In contrast, the ex was not right for me, and we were very dependent upon each other emotionally, which became unhealthy. 

But, I could work on him now and he would come back because I don't care now, although I won't.

Good luck!