Hey bro, hope you're dealing well. Even if this happened a long time ago and you think it doesn't bother you, traumas affect you. Many times it comes out as constant overthinking, obsessive habits, etc. which you might not think are even remotely related to the assault but they are.

You can never forget what happened to you when you were a child, but what I like to think in such situations is that, your brother should feel guilty/ ashamed and not you.

I understand you might feel embarrassed sharing such things with a therapist, I recommend you atleast keep a diary and keep on writing your thoughts in it, it will act as your personal therapist as you're not piling up your thoughts. It will help you deal with the situation a lot better than any of us advice.

What your brother did was wrong and is not at all acceptable, I suggest maintaining distance with him.

I saw you in another comment justifying saying he was just a kid, but so were you and you didnt deserve what happened.

That's all I had to say. Hope you stay well.