I went through something similar years ago, and I agree with other's advice here. You just need to move on, even if it means cutting this person out of your life. That's what I did, and it was the smartest move I made. Today, I'm married to a great guy and I can't quite remember what I saw in my old friend, but when you're first going through this, distance is the best medicine.

read The Prophet by Kahlil Gibran, for starters, and get a spiral notebook (I prefer wide ruled) and make time every day to write down your feelings. Any situation is easier to comprehend looking at it on a piece of paper than peering into the infinity of your heart. In three months, read back over it, and again in another three, and another three, and...
Life is an exercise in love, become a student of it.

How do you know she does not have the same feelings as you do. Is she committed to someone else? It is easy to have strong feelings for someone your so close to. If you have talked to her and know this for sure, than maybe you need to focus on your future and see less of her. You will find the right one, be patient.

Agreed. While it probably feels like you can't imagine life without her, you should cut communication. I've been in your shoes and while it was hard, it was the right thing to do. I got to pursue things I loved, meet new people and best of all, fell in love again (that last one took awhile.)

I'm sorry you are hurting, but you will find another side of all this!

Move on. Find what you like best about yourself - and draw the strength from that to move on and uncover other opportunities for yourself. Even if it doesn't feel this way right now - there are many other people out there who might be an even better match for you. And it might be a good idea to minimize the contact with your best friend for the moment ..