To make this change will require deliberate effort. There is no easy shortcut. When you allow your thoughts to return to the loss and look for him to return, it doesn’t give you the chance to grieve. Breaking up is difficult, but ruminating about it can be even more devastating. If you want to feel better you will need some support to make the change. Reaching out here to PsychCentral is a great first step. The way to follow this up is by finding a support group or individual therapy. As far as books are concerned I like the daily meditations offered in the book The Language of Letting Go. They can be applied to your situation and will help you untangle from your ex.
Wishing you patience and peace,
Proof Positive Blog @ PsychCentral