Right now your just being stupid.
You said his family treats him basically like shit. He might need some people to actually be there for him.
Your going to ruin your life to "help" someone elses. You don't know what reasons he has to join it but obviously it's something that he decided to do. You can't go off the babysit him. It's like getting a girlfriend in middle school. You think you love the person but there is a high probability your not going to get married. With you and your friend; He is your best friend? Your both not going to be successful into a millionaire franchise and at the rate your acting I don't think either one of you are going to be. "If I get killed its my fault" Your fault for being a dumbass. Just let him do what he's doing. If you were a real friend you'd let him choose his own path whether it be gang life, prison, or death.
But hey, what do I know. I'm only 15.