How do I tell him....?

I am incredibly heart broken. I fell for this guy about 5 years ago. At first, I admit, it was nothing more than a simple crush. But, a year past and that crush didn't go away. Meanwhile, we were becoming better friends. To cut to the chase, we ended up becoming very close about 2 years ago. By this time I knew that I loved him and I was on the brink of admitting that I was in love with him. I was scared though. Scared of getting my heart broken by the one person that mattered most. Now, I still love him. More than ever. He is always on my mind and I honestly care more about his well-being and happiness than I do my own. I would give anything in the world to be with this person. I would even die for this person if need be. As of several months, it seems as though he is beginning to have feelings for someone else and it is literally killing me. I don't eat, sleep, or act normal anymore. I want to be able to express the love that I have for him without annoying him or scaring him off. If he knew just how much I cared about him, I think things would be different. Please help. Any advice would be helpful. Please.