I know I'm not the best at advice but if you haven't told him how you feel, you definitely should. I have a best friend to and he's a guy. I've liked him for a while and he has a girlfriend. I wish I could tell him how I feel without ruining the relationship, but I have to wait for the right time. You seem to be pretty close with this guy. I think you should tell him what you think about him and how you feel... That would let him be on the same page as you.
Thanks for commenting and saying thanks!