How to let go of the one you loved?

It's clear now I messed up with this girl. I should have kissed her but always had to 2nd guess myself. I know I'm confident in my conversations and could have gotten about any other girl in this situation,but she had that something that made me act like an unconfident scaredy cat. I mean I have had crush on her since high school school and she was the first girl I reallly really liked. I would do almost anything to win her back and be her friend again, but clearly that's not going to happen and there are better matches for us. It hurts thinking about it knowing that if I played it right it could have been really really special. She said we could have been "the best ever" and I can't let that go. It's too late now cause I called her every bad name in the book and she won't talk to me. What's some tips to dim the pain of messing up with a girl you had fallen head over heels for?