Have you tried volunteering? It's a great way to get your thoughts off yourself.

Also, you need to use what I call "stopped thinking", It's what helped me overcome sort of the same obsessive thoughts. Every time I would start to think of that person I would say "stop thinking" and think about something else. If the thoughts persisted I would do the same thing again. If I was alone I would say it out loud. It takes time, but you have to give up the fanatsy life you have developed. It's not easy, but you can do it.