logbrock, could acceptance play a part here?. have you accepted that he's an addict and for has made a decision to move on? are you still hoping that he changes his mind and come back? have you accepted that your life would be easier if addiction wasn't somewhere lurking?
trust me, i know the obessive thoughts, changing those thoughts is not easy to do but not impossible, maybe having a conscience awareness of your commitment to do so, you can do it. you'll find that day by day, you'll began to think about him less and less, so with the pain, it began to hurt less. the sooner you start the sooner you'll began to feel better.
i found reading a good book out loud to myself help, cleaning closets was what i liked too. i'd actually lose thoughts of him in doing these things. there were times i HAD to go somewhere and just people watch, it helped me to focus on something other than my ah.
for now try to just accept the fact that he's gone. do it one day at a time. repeat after me " today i will not think about him all day, i'll do it tomorrow if i need to". tomorrow comes, repeat. one day at a time, you get there, i promise.