Okay, I always thought you were actually 13 before, but I'm not so sure. If you're 13, then you're right, he's going to be mad at you, and he might stay made at you. Younger teenagers are aren't mature enough to deal with some things. On the other hand, if you're older, it's a lot more possible he can deal with it. In either case, it's possible that he values your friendship over the the band position. He should respect that you want to be in the band, too. It'd be nice if you suggested he be in the band also, but if that's not possible, then he's got to understand. If he's a real friend, he'll still be your friend either way.