What should I do? Friend saying 'good bye'?

So I have this friend who told me loves me so much. I have some feelings for this guy yet I am still not ready to say the "L" word or to be in a relationship because I feel that I am still young. He gave me a 'farewell' letter saying that he wants to move on already because it kills him not to be with me. He also said that he was jealous of this guy friend I have who posts on my Facebook wall (Believe me, we're just friends). I KNOW that he loves me so much - it's quite obvious. In the letter, he remember almost every little thing that we did together. And when he said good bye, it hurt me so much. What should I do? I feel devastated when I lose my friends (specially this one since he is special). Should I just let him move on or try to talk to him? If I talk to him, what should I say? Thank you.