Is it appropriate to write him a goodbye note?

Here's the situation...I met this guy almost three years ago. I would say he's my best guy friend. I have gone on a roller coaster where I like him more than a friend, then I don't. We occasionally sleep in the same bed, but not too much monkey business has happened. About a week ago I told him that I still sort of had feelings for him. I went through a really dark period this year and he helped me through it more than anyone else. I am moving home(Milwaukee from Minneapolis) in a week and a half and was wondering if it's appropriate to write him a letter thanking him for being there for me and telling him I am going to miss him? I am going to be gone for over a year.