Most Helpful Guy
There isn't an easy solution to this. I am in a similar situation (reversed, because I'm a guy), I only see two solutions: 1. truly get over that person, to the point where you go days without even thinking about him/her; or 2. Find a way to make him change his mind and be with you. Option number 2 isn't as ethically sound as option 1, but it's still possible.
I see two ways to accomplish option 1: a) find somebody better, or b) cut that person out of your life completely. Both are difficult, but those are the only ways that you will be able to stop thinking about him.
You have my sympathies; I really really know what this is like.