@Jessy I am unfortunately all too familiar with the sort of situation you have described. It is pretty much an all-or-nothing deal, because if it works out, that's great - but if it doesn't you essentially lose a friend AND potential lover. Not a good place to be, I know.
My advice is to value your friendship first. Be the best friend you can be to this guy. Be honest with him, and find little ways to simply let him know you care. Small gestures which show that you pay attention to what he likes may not seem all that effective, but they do get noticed and appreciated.
Don't hold a boom box blasting out Peter Gabriel's "In Your Eyes" above your head as you stand outside his window - this only works in the movies. In real life, all it may get you is a citation for disturbing the peace.
I'm not sure by how you've worded it whether you've known this guy for three years, or that you've been in love with him for three years, and have known him longer than that. Either way, you should have some idea how he feels about you by now. Is he happy to see you, or glad to hear your voice when you call him? Does he seem to enjoy spending time with you? Will he tell you things he doesn't feel comfortable sharing with others? Think back to how he has acted in the past, and pay attention to how he acts now. You may discover he admires your you-ness more than you know. If that's the case, a little encouragement may be all he needs.
On the other hand, if all he wants is your friendship, that realization on your part will be painful for a time, but if you have to accept that you and he are destined to be good friends, there will come a time when you will know it all worked out for the best. There are worst fates to be had. Believe me, I know.
