Is it normal to think so much at one girl

I have a girlfriend i really care about. She used to talk often to me but she sudenly stopped and now we rareley speak .I now often think about her and it gets quite annoyng.She is really goodloking and friendly but she doesen't seem to be friendly to me ,even thoug she really was before. I don't undersant why.I often think of her as a friend but also i am sexually atracteed to her. Can you give me some advice to get rid of this crush or something please!!