welcome to the forum. You seem to have processed a great deal of what happened to you. I think whether we are physically hurt or enjoy it at all, being introduced to sex at an early age is traumatic. It certainly sounds like it strongly influenced you to regard sexually pleasuring your brother as a favor, and you didnt get a choice in who your first sexual experience was, which is also unfair. In all those ways it seems clearly traumatic and abusive to me. I'm sorry for that. I'm very sorry it created so mcuh confusion in your life.