If your mom/dads has a new partner, are they considered your “new family?”

When my late dad started dating (let’s call her Stella), after being single for four years, I didn’t like it at first. I hated when she came over. I wanted my mom and dad to get back together but my dad flat out told me straight that it wasn’t going to happen. I did a lot of things to break them up but my dad always wins. So after a couple of months dating, one of my aunts asked me a disturbing question: “So how do you like your new family?”
I gave her a look and said, “New family? They are NOT my family.” My aunt says since dad and Stella are dating, they’re part of the family now and it was time that dad found love again and I’m getting older. I was 11 going on 12. Change was difficult for me and it took me YEARS to accept it. I hated it. Her kids grandkids would come over a lot and bug me, even if they said they love coming over. She would come over every weekend to spend time with dad and sometimes the kids come over. I loved it when it was just my dad and I. My siblings told me that I need to stop interfering with dads relationship and back off. He deserved to be happy just like they had to deal with the same thing when my mom and him first started dating. We’re half siblings. They said I needed to accept it and they’re part of our lives now.
They dated for eight years before he passed. Stella still talks to me.