Should I write a letter to him?

There's this guy I like named Curtis and I think he knows I like him, but I don't think he likes me. So, I want to tell him how I feel about him without embaring him. Last night, I was thinking about writing a letter to him telling him how I really feel about him, but for his sake, I want to just be friends. What should I write? I am way too shy to tell him to his face. He's so close with my friend Kaitlin and her two sisters and brother. And I want to be that close with him, but the only way I can do that is by being his FRIEND, not his STALKER. So, should I write a letter and what should I say?