First of all, you need to identify your feelings towards him, then let them go and release every bit of tension in your muscles.
It helped me, when i wrote every word down that came into my mind when thinking and focusing about my ex-girlfriend.
In my case, my friends over at hunatrainer.com bbs helped me alot - here is a link to the thread, it probably doesn´t make much sense to you if you are not into huna.
HunaTrainer Bulletin Board : Huna Forum :: View topic - Forgetting about Ex-Relationship