If she doesn't have feelings for you anymore besides those of a close friend, you have to do what's best for your relationship and respect that. I know how torturous it can be, being so close to someone you care about so much and not being able to express it, but if you really care about her you'll preserve the good friendship you have now.
On the other hand, she may have feelings for you still but is hiding them because she's afraid you don't feel the same way- ohh how many times I've seen that happen. And in my experience, girls have always been better at hiding their feelings than guys
So you need evaluate the possibility of her sharing your feelings. We can't tell you what she's feeling, obviously, so it's up to you to figure that out. Pay attention to the little things she does and says- does she flirt? Do you catch her looking at you sometimes? When you're together, does she stay really close to you or keep her distance? Look for little subtleties like these and decide if you should take the leap and confess or remain quiet.