Well... why is he your ex? There must a reason! I had a problem similar to yours....I was dating a guy and couldn't stop thinking about my ex.... not because I wanted to be with him anymore but because I just couldn't stop thinking about my new relationship in comparison to my old....
Well... do you really want to be with a previous cheater? You deserve better! So friend him, stalk him, and realize why you two ended it.
Haha, its cool. My long time ex I always think of friending him on fb or myspace but never do because I really don't care what he does... ya know? And I don't want to get caught up in all the stupid drama. You'll never forget him Just let that be known. I will never forget my ex, ever. So decide which of the two evils you want to battle