Yeah, I can understand why you'd feel emotionally conflicted and repulsed by what happened back then, because you're a responsible adult now. But you have to remember you were kids, children, back then, even when you were young teens (I'm assuming your brother is two years older than you, max). It's very normal for children to be perhaps exploring and wondering about sexual matters because it's something they observe in the adult world frequently: tv, magazines, things in society in general etc.

Anyway, I just want to say you're not a 'freak'. You did nothing wrong, and you're not that innocent child anymore. It's time to let go and heal your inner self now.🙏