I always found myself fantasising about a friend who confessed to me two years ago. Problem was, I didn't like him at the time. During these two years I've had on and off periods where he would enter my day dreams and I would have to keep reminding myself why I rejected him in the first place. It never worked of course, and in my fantasies, his faults were non existent, and he became the perfect male. I let my imagination run, until recently when I bumped into him again. Quickly, I was once again reminded of why we couldn't be together, and everything was put into perspective after a quick chat and a "See you later." I stopped thinking about him after that, and decided I would busy myself with things so I would once and for all forget about him whilst in a reality check period. So far it has worked.

Fantasising about ex's would be the worst thing to do because you start painting a perfect picture of them. My advice would be to keep yourself busy so that you don't have enough time to think about it. It's like cutting a bad habit, the first few times is hard, but soon, it becomes a smooth road from there.