Your sexuality is not determined by what arouses you
it's part of it, for sure, but sexuality is also about relationships and stuff. It's all pretty complex, so it's doubtful you could get the right answer at 13, so the chances are you just like your friend because he's your friend or you feel comfortable with him. But mostly, it's all about hormones. Think about testosterone as gasoline and your body as the fire. All that gas suddenly hits your body at puberty and *BAM*, everything's sexual!