My mother wants me to call her husband Dad

Dear Delyara, My mother remarried when I was thirty-five. Her husband is kind to her and has never treated me badly. Last week, she asked why I still call him Robert instead of Dad. I thought she was joking. She was not. She said my father has been dead twelve years and Robert has “earned the title.” I became angry enough to leave dinner early. My father was imperfect. He drank too much, forgot birthdays, and sometimes disappeared emotionally for weeks. He was also the man who taught me to ride a bike, sat through every school performance, and called me “kiddo” until the week he died. The word Dad is not a promotion awarded to the best current applicant. Robert does not even want it. He called afterward and apologized for my mother. That made everything worse because I like him. I want my mother to be happy with him. I simply cannot participate in rewriting the family so her second marriage feels more complete. She says refusing the word keeps her living in the past. I think demanding it asks me to bury my father twice.