Good guy friend turning into lover?

I have had this friend for just under a year. I met him thru a friend last semester in college because at the time she liked him and they never dated but hooked up and then just became friends. Ever since we all have become super close friends i even nickname him we all make fun of him its a lot of fun together. Over the summer (we dont live in the same state) we kept in touch he is an extrememly flirty guy to literally every breathing girl on earth...BUT we are really good friends. He is there for me in any situation he listens to all my crap gives me advice..has dinner with me acts like my brother best friend. We flirt and act that way because we are both the types of ppl who are dirty and horny all the time. We have similar personalities..etc. Lately when he gets drunk i notice he will kiss my head and progessively it gets more..he now smacked my *** and said were unconditional lovers..i am confused because im sure he could and maybe does like me..i could like him back but will that ruin our friendship? my friend who used to kiss him will b weirded out cuz hes liek our brother pal? also i see him as nerdy some days and others like a potential....what is this next step??