How can I tell if my friend is gay ? Are these signs?

I have a friend who is different from my other friends, like...he's sort of flamboyant. From a distance If you see him walk , you would think it was a girl. His voice has that gay accent(no offense to gay people) but you know the type of voice im talking about. He's one of my bestfriends and if he's gay I don't want him to feel like he has something to hide because it's really obvious , even my parents think he's gay. When he's not hanging at the skatepark he's with alot of prissy and girly girls, its like he has more fun with them then us guys. I joke sometimes and tell him that another guy has has a crush on him and he gets pissed. I can't really decide, he has had girlfriends. One of my friends is talking about outing and I don't want that I just want him to tell me...