Why do I still care about my exes?

I have been with my current boyfriend for about 6 months and we are very happy together. I love him a lot and he really is the best boyfriend I have had. But for some reason, I still care about my exes. I don't care about them like in a way where I am like calling them to check up on them or something but for example my most recent ex just got a new girlfriend and it bothered me SO much. And I am sorry to say that I I guess "Facebook stalked" her and I checked out her pictures and things and I got so jealous of her! And when I find out my other exes have other girlfriends that makes me kinda upset too. I don't understand why though all the relationships ended with me hating the guy and now I have a great guy so why do I even care about what they do now?
Why do I still care about my exes?
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