Why am I jealous of all my exes girlfirends....?

Okay, I have two exes that have moved on from me, and got new girlfriends. I have a boyfriend who I've been with for over a year, I love him to death by the way. Out of curiousity I check my exes myspace pages, see their girlfriends, and get super mad, I don't know why I still care so much.Especially when they don't, I guess I get mad becuase it looks like they treat them way better than they treated me when we were together.Help, why am I like this?