Hi there, you are not alone. I was physically, emotionally and sexually abused by my sister. She used to beat me up almost daily, calling me names and bully me all my childhood and teenage years and sexually abuse me. It was very humiliating as I was the older brother. She had found out about boys’ sensitive part and kicked me there regularly. My self-esteem was very low, especially around her. Although people saw the physical and emotional abuse, they thought it was just sibling rivalry and laughed about it. They also blamed me for being a “sissy”, “not being a man”, etc. as I was 18 months older than her.

I had really difficult teenage years and my twenties were pretty bad due to self-abuse. Eventually, after years of therapy, I managed to stop or reduce the self-abuse. However, i started to get huge sexual gratification by re-enacting the fights, the verbal name calling, the sexual abuse scenes, etc. I have tried to deal with it by therapy and it comes and goes. At times, especially if I see here (which is just a couple of times a year), I even hire escorts to re-enact the fights (I am gay so male escorts).
Try to deal with it sooner as it may affect your relationships.
From what I have heard, it is a coping mechanism to deal with something so traumatic.