Can someone HELP...boy problems?

[Hello]

Okay this leads on from my other question....basically I am still not over this boy that I talked to for 9 months! Again we had one of those "we almost dated" things. But anyway, I was over him then liked him but I cannot go one day without thinking about him in some way. I don't know why I care so much because I know he doesn't even think about me like that anymore. Also last night my friends decided to talk to him and I got really annoyed and jealous, all my friends talk to him and I don't like it so I don't say anything. Basically my question is why I still have these feelings, and what can i do to stop them and prevent the jealously that has built up!