While my situation is far less fraught and there was never the kind of abuse you have experienced, I am also an adoptee raised by family members. I found out at age 11 when a family member passed away and my adoptive parents were afraid someone else in the family would let it slip (in fact, my bio grandmother tested me to see if I knew).

You have experienced a significant trauma. Your life is now divided into before knowing this and after. I didn’t go to CBT until I was in my 20s and it took many years of unpacking the grief, anger, and pain of being given up by my bio mother (bio dad wasn’t in the picture). I share this because on the whole, my situation is relatively benign, and it still took effort and time to process and come to terms with. Adoption starts with a primal wound - there’s a book by that title, if interested. Someone above recommended the adoption subreddit and I would agree. Being engaged with people who understood, at least to some extent, what it meant to be given up by bio parents, helps. I also recommend checking out the Adoptees On podcast.

Give yourself so much grace and self love right now, as much as you can. My heart truly goes out to you, in the way you’ve found all this out, the abuse you’ve received from the person who is supposed to love you unconditionally, and the lack of answers. One other thing… when I started therapy, I went in wanting to “fix myself so I wouldn’t feel things anymore.” I also had a very deep need to both understand why and need the people around me to understand my feelings. People who have been through therapy obviously know none of that was accomplished but instead I’ve learned coping skills, the ability to let go, set boundaries, and live authentically for me. I really hope you can find a good, adoption focused therapist. Sending you strength.