My dad died when I was 7 years old. He was my favorite person, my mom's favorite person (at the time) and I kind of think he was the person who could compliment our personalities enough for us to be super close. Even as a little kid I kind of knew that. It broke the two of us when he died. But then she found someone else, she found Luke.
She married Luke when I was 9 and he became her person. Luke, upon realizing my dad had been the parent I was closest to, tried to fill that space, and was unwilling to listen when I said that space was reserved for my dad. It caused some tension.
Over time I let some things go. They would call themselves my parents or my mom and dad. I always called him Luke. I always told people close to me about my dad and would make sure it was known Luke was not "dad".