Is it dumb to be sad over a girl?

I really liked one girl. She liked me too. We became closer and things were looking really good. We kissed few times and we went out. From what her friends were saying i was sure we are going to be together and it is just matter of time. But then she turned me down. It was 7months ago and I am still not over her. I dont know what I did wrong. It really hurt me cuz I was never into someone as much as to her. I dont think i will ever have a chance with such a pretty girl. Is it dumb to be sad because of a girl?

Is it dumb to be sad over a girl?
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