I can't remember much but the world is divided into subs and doms even as children they are separated into schools to teach them to submit and dom. I can't remember who is who but I think they don't understand why it's this way or they realize they're the other??

I do remember one of their parents are in a sub/dom marriage

I also think the sub saw a dom being harsh to another sub and that Dom commented on how one of the boys treated theirs?