How to get a girl out of my head? She has a boyfriend now.?

I've been pretty good friends with her for a while, and was actually thinking of asking her out but I never mustered up the courage. Anyways this summer we were going to see a movie and I had planned on finally bringing it up, but she kept cancelling on me and I haven't seen her since. I deleted my facebook recently but my best friend said her relationship status changed to "in a relationship," and i texted her about it but she never responded. We used to text basically every other day and hang out once or twice a month, it could have been more but we go to schools in different cities. We rarely talk at all now and when i try to text her she hardly ever responds. Anyways I just can't get her out of my head, if you guys have any advice that'd be super great, thanks.