If he thinks your friends and you start to flirt with him hell probably be confused but if he likes you too in a non friend way just give it a few days to a week and just tell him you like him or you might not ever go anywhere with it unless you feel like your friend ship is more important cuz if it doesn't work out that friend ship will probably never be the same again cuz thats how it was with one of my best girl friend
Theres no problem in being in love with your best guy friend, since hes been there for you through the thick and thins and you guys known each other for a while right? I'd say you should slowing start showing him some signs that your starting to like him and stuff.
You have to find out if he feels the same way about you or not?
Try to flirt. Start to do it casually and grow until you think you are ready to ask him out.
Just play cool and flirt or give hints that u like him but not to much.