Why does it still bother me?

Me and my next door neighbor broke up 3 months ago and not even a week later he was already dating someone else. This girl visits him regularly and stuff so it's something "serious". The point is that it really hurt because for the first time I believed I could fall in love but I was wrong. After that I found out what a jerk he is ( His sister told me some fu*ked up shit about him ) . I stopped saying hi to him, I stopped looking at him in the eyes.. but lately I've been thinking about him way too often. I feel so dumb because I even told him I was a virgin and I can't stand the fact that this stranger knows it. Living next door is not easy at all, it annoys me so much because whenever I go out I dread meeting him. Why is this happening? I know losing him was my biggest win but I don't understand this nostalgia now
Why does it still bother me?
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