How to know if ur best friend is gay ((without telling him)) ?

Any signs?- Hi - btw: he likes death metal music and ( the style,,long hair..black eyeliner..) and rock ( so i don t think he is gay):D -and always try to be cool -and he likes harror movies (saw..) but sometimes he acts girly , he likes to hang out with girls more than guys our friends ( but he doesn t show that he likes,,), he didn t have any gf before (or now) ,, - i don t feel he is gay when i am arround him but sometimes @ home from skl , i think ,,,,,, that he is trying to hide something with being cool,,, and maybe he is ,( dunno! ) so what do u think ( gay or,,) ? and what to do? :D thx ( for reading and answering :P )