How can u tell if a guy is gay?

i think my friend that i havent seen in awhile is gay i (used) to like him last that i kno he had a gf and just so u kno im a girl lol i dont wanna believe he is but i have a feeling he is i really (used) to like him to he hangs out with alot of girls but in a playa playa kind of way but when i looked into his eyes its like somethings not right and like hes hidin something