I'm in a similar situation to you. however, she is intereted in someone else. she knows that I have feelings for her, I told her. she refused to date me. Right now, we are closer than ever. I still am the good friend I was to her.
She realizes how much I care about her and how much she means to me, but there is nothing more than friendship.
There is a good side to it; having someone of the opposite sex so close as a friend.
In my case, I try to be rational and control my feelings. I try to hide the expectation of her changing her mind deep inside. I think for a guy, the most painful thing is knowing that a girl is interested in you and the hope of being with her one day haunts you day and night.
My advice is to move on. Find other people who you are interested in. Forget about the thought of maybe one day you will be with her.