How do I know if my guy friend is gay ?

Okay so , I've known this guy for 2 years now , we're both gonna be juniors in high school this fall . Anyways , when I first met him , he was super nice and (we met during cross country ) after a few weeks I discovered he didn't hang out with guys other than his younger brother . Then , freshmen year came and we kind of got out of touch since I didn't have any classes with him but I saw him everyday at practice and we'd talk and his voice was very soft and girlish ! There are also these popular girls on our team and they love teasing him , but he gets very shy and kind of avoids them or hides behind me . Sophomore year we had 4 classes together and he got mean but he would be sentimental at times and apologize . I realized he really enjoyed messing up guys' hairs and he acted kind of mousy around them . Keep in mind that he had several friends who were girls : me , J , J , and N . We were his "true " friends and he was pretty mean and abusive to us but he'd also be nice and show us his deep voice . I apologize for the lack or organization in this question but it's been on my mind for so long ! And , his cousin wants US to go to junior prom together ... I once asked him if we likes girls and he said no but during elementary school he liked his one girl but I don't know if he's lying or not . So , help please ? No trolls , thanks .