I think if a chick has a guy best friend, she has a little crush on him. I mean, I kind of have a crush on my best friend (who is a guy). I of course WILL NEVER tell him cuz it would be VERY VERY awkward.
He doesn't have a girlfriend/boyfriend or anything, but it would still be a very peculiar situation. When I tell him about my relationships, or guys I sleep with, he doesn't get angry or anything. He just gets irritated and says I am stupid for doing that, lol. He's really just watching out for me, though.
And yeah, he has commented on my appearances. He says that I am pretty and could, for the most part, get any guy I wanted. And when I complain about feeling fat, he says I'm not, blahblahblah. Everything a best friend should do to comfort their best friend.
But, your approach to him is totally up to you. If it's not TOTALLY serious, then don't say anything. And, also, try to talk to him about his girlfriend. Ask why he doesn't split with her. Things like that. It won't seem weird cuz you're his best friend, so yeah. (:

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If the doors of perception were cleansed every thing would appear to man as it is, infinite.