I’m worried that if I respond to my sister's questions, it will hurt her feelings. What should I do? (W: Abuse)

(References to abuse) I’m a 50-year-old woman and recently shared some negative thoughts about my life on Facebook, specifically regarding my sperm donor (71 years old), whom I’ll refer to as SD. My sister, who is 45, responded by asking why I couldn’t simply “let things go and reconcile.” To give some context, SD has always exhibited classic narcissistic traits, including a quick temper and an emotionally abusive demeanor. To me, he was physically, mentally, and emotionally abusive, alternating between cold indifference and outright neglect. Being the older sibling, I felt a strong responsibility to protect my younger sister from him. My sister was viewed as the “golden child.” She thrived in her father’s eyes, engaging in traditional “boy activities” like fishing, hunting, and sports. I remember hearing SD express more than once that he didn’t miss having a son because his little girl more than filled that role. She adored him, almost to a fault. In our upbringing, the difference in treatment was stark. While my sister faced rare instances of spanking or yelling, I endured far worse. I faced physical punishment, slaps to the face, bullying, and constant belittlement, sometimes even being locked out of the house until our mother returned. Academically, I struggled, particularly with tests, resulting in below-average grades. My sister never witnessed the depths of SD’s cruelty. The most brutal incident I experienced occurred when I was around 12. After he falsely accused me of lying and I dared to defend myself, he grabbed me by the jaw and lifted me off my feet, holding me suspended in the air. I remember hearing cracking sounds, convinced he might actually kill me. Once he finally released me, I escaped to my room, living on soft foods for weeks and lying to our mother by claiming the injury happened on the playground. I knew that revealing the truth would subject me to an even harsher reality. Ultimately, a visit to the dentist revealed that he had cracked my lower jaw and partially dislocated it, leaving me with ongoing issues related to that incident. My sister has never known the truth about what I endured. I never wanted her to—she deserves to have her hero. However, she’s now pushing me to reconcile, calling me “self-centered” and urging me to return to the family. I find myself grappling with whether to tell her the truth and risk ruining a relationship she cherishes. Complicating matters further, she has two sons, and SD is a good grandfather to them. Meanwhile, due to SD’s influence, my sister and I were estranged for years, and only in the last seven years have we attempted a reconciliation. Part of me feels that maintaining the status quo, as I have for so long, is the best course of action. I’m resigned to being seen as the “bad kid” to spare her any discomfort and preserve her family life. My own situation feels irreparable. Should I keep my silence and potentially safeguard our relationship, or risk everything by revealing the truth? Additionally, I’d appreciate hearing from anyone who has experienced similar abuse. I’m simply seeking different perspectives. Thank you for your time and insights.