Is this something I should be concerned about? I think I caught my brother’s gf in a weird position while I was taking out the trash.

I went to take out the trash when I heard some moaning from the room across the hallway from where I was. I immediately stopped taking out the trash, grabbed the trash bag and just stood there listening to the moaning which got louder. I didn’t think much of it at first, assuming it was my brother and his gf doing the deed. It was only when the woman started screaming that I knew something was up. I immediately ran in to find her in some sort of weird position with her back towards me, on her hands and knees, and my brother behind her. I didn’t see any penetration but I saw my brothers erect penis which was entering her. I didn’t see her vagina at all, just his penis going in and out. I didn’t say anything, and I didn’t leave the room, I just stood there frozen. I didn’t see her face but she seemed to be in pain by the screaming she was doing. I didn’t say anything because I didn’t want to ruin their moment but I did ask “are you okay?” I heard her say “yes, I’m sorry” but I didn’t hear my brothers response. My brothers response I did hear was a loud “oh shit” as he heard me. I told my brother “I’m going to go back to my room now” and left the room. I was terrified and still am. I don’t want to tell my parents but I don’t know if I should. I feel like they should know that my brother is hurting his gf but at the same time I don’t want my parents to hate my brother for the rest of his life. I don’t know what to do. Please help.