I have no personal experience with this, but I'm sorry it happened to you. To be betrayed by family in this way is just despicable. I can say though that you have nothing to feel guilty about, you were the one being exploited and abused, if anyone should feel guilty it's your brother.

I wonder if there's a way to train your brain to connect a woman's body with something other than the abuse, perhaps by trying to think of your wife/girlfriend or just the best sex you've ever had with a woman, something to disrupt the thought pattern.

Have you ever confronted your brother about this? Sometimes confronting our issues head on can help us overcome them, and he needs to know how much his actions effected you by exploiting your trust in the person who was supposed to always watch out for you and have your back.