AIO for cutting my brother off and going no contact?

This has been plaguing me for quite some time and I need some outside perspective.

When I was younger, around 4 or 5 years of age, I have explicit memories of my brother (13 at the time) making me perform oral on him. I struggled all throughout my childhood with depression, self harm and suicidal tendencies. I feel like his actions gave me a lot of trauma that went unchecked.

I have cut him out my life, we have 0 contact.My sister mentions him a lot and just hearing his name triggers me. It upsets my sister, she wants us all to get along. She says because he was abused too, he's also a victim and his actions weren't his fault.

I told my sister that I would not be comfortable if she were to bring this subject up with my brother but she did anyway and he confirmed he remembers.

Am I over reacting to want 0 contact? Is what he did even that bad? I have read a lot of things on here lately that this sort of thing is common and normal?