User post: Why would you try to get in contact with an ex?

I had been dating this guy for close to a year, when last November he decided he wanted to move back home... in Texas. We initially called it quits, but then decided that we should try the long distance relationship. Meanwhile I did some snooping around and found that he had started seeing someone new. Of course I confronted him about it and that's the last I heard of him. Fast foward to last night when I was reading my e-mails, I found a new entry from him. The e-mail was brief, and went somewhere along the lines of "I'm sorry, how are you?"

I heard somewhere that an ex will always come back to you. When I look past at my relationships I find this statement to be sort of true. But why? Why do they come back? And so out of the blue? Some come back with the hopes of salvaging the past relationship, others just to see how were doing. I'll admit I'm the kind of person that cannot remain friends with their ex's, so it baffles me as to why they would try to get in contact with me.

So.... my question is: "What motivates them to get in contact with you?"