ADVICE: How do I stop thinking about someone who abandoned me?

I dream about my ex all the time even though he abandoned me while I was pregnant and treats me like I don't matter. How can I stop?

ADVICE: I ruined a great relationship...what do I do now?

How can I accept that I've ruined the best relationship I've ever been in? Insecurity and self-doubt got the best of me. He was a pretty great person. I hate myself now and am trying to work on myself. I know I need to let go of old baggage, but how do I cope when I know it was because of me?