I was raised by an orphaned father. His mother died when he was 3, his father died when he was 9 and his only sibling died when he was 18. All died from TB. He never discussed it with any of his children. Finally, my mom forced me to ask him about it in order to write a paper for school. He told me. I could see it made him very sad. He never spoke about it again. A few years later, one of my brothers was diagnosed with a terminal disease. My dad was devastated. In retrospect, it was his past haunting him again. He died before my ill brother did. I have heard similar stories of holocast survivors who would not discuss their pasts with their children. Perhaps you could help him grieve. Are your grandparents' graves nearby? On mother's or father's day, perhaps you could ask your dad to visit them with you? You could also ask your dad about them since you never met your grandparents. Ask him what they were like. What his childhood with them was like, etc. All the best to you.