It slightly hurts... it does, why did I have to feel this way? Why?

I know that my feelings for him are already gone, but... why? Why does it hurt? I can’t understand myself, really...

A while ago, when she said that she liked him and when I found out that another girl likes him, I slightly felt hurt even though he’s just a friend to me now. I hate this kind of feeling when you know that your feelings for a someone is gone but then, when you find out that some girl likes him, it’s like this selfish and jealous part of you comes out and you start comparing yourself to other girls. ARGH! I hate this feeling! I want it to disappear, can someone please help me? I really need help! ARGH!!! I don’t want this kind of feeling! I better stay away from him as soon as possible or else I might fall for him again. :’(