I feel really guilty and confused. please read?

I was watching a movie with my best guy friend, then I was falling asleep. He then kissed me and I pulled away in shock. I really didn't see that coming. I feel really guilty cause He was really down the rest of the night and I was trying to cheer him up. It's not that Im repulsed by him, I would like him that way if he was a bit more mature. But I just don't right now. He's like family to me. What do I do next time I see him? Should I just pretend like it never happened?