Im worried my little brother is being abused

My mom has always been extremely insecure. She wants to be #1 is someone's life. So she would date men who would shower her with life while abusing me. She watched them beat me but didn't care. She only ever left if they started sexually abusing me because to her that means they love me more. I left home at 16. When I was 20 she got pregnant with my little brother. She left his dad because his dad loved my brother more. As he should. My mom has been dating this guy for a few years. My brother is 15 and whenever this guy is around my brother is super quiet. Whenever I mention my mom or her boyfriend my brother kind of shuts down a little. He was day dreaming and I touched him and he had pure terror in his face. It took him a minute to cone to. I'm so scared my baby brother is being harmed....

Edit: I don't pray for my mom(or in general) she can go fuck herself.