Im a 17 year old guy, and I like a guy, what should I do. I cant tell him. Please help me out?

Before revealing your feelings to him, find out what are his feelings for you. Just a friendship or love. Ask him if he likes someone. He's your only friend, and he is nice to you, you could ruin that if you tell him you like him, not because he will like stop being your friend but things will get awkward and things for you will get worse. If he doesn't just keep your friendship with him, try to get over him