Feeling crushed by childhood trauma and guilt I don't know how to shake. Anyone been through something similar?

I am 26 (m) now and recently had memories coming up that mess with my mind. When I was young, I was sexually abused by my older sister. Later on, I saw my cousin brother abusing her too, except it looked like she went to him willingly. Seeing that made me feel this weird, messed up jealousy because she was so close to him.

Because of all that confusion, later on when I shared a bed with her, I ended up touching her. My whole life growing up has been completely messed up because of these cycles.

I honestly do not know how to get rid of the guilt. I have done things I am not proud of, and it makes me feel sick. I just want to know if anyone else has been in a similar situation or how you even begin to process something like this.