I really like a girl that I have known for a few years, and I just can't get her out of my mind. I can't concentrate properly when working, and I just can't get on with doing college stuff because I just stop and think about her. I haven't told her I like her but I think she knows anyway and I'm too scared that I'll lose her altogether if I tell her I like her. Why am I thinking about her so much? And how can I concentrate better and stop thinking about her?