AITJ for cancelling a family holiday at my house after my dad said he was bringing his new partner and we all had to “accept it instantly”

I 28F offered to host our big family holiday this year for the first time. Usually it is at my parents place, but my mom moved out last year when my parents separated and the house is smaller now. I have a decent sized apartment, a dog, and actually like cooking, so I thought it would be nice to have everyone over and also take some emotional load off my mom. When I first floated the idea in our family group chat, everyone sounded excited, including my dad. The only thing I asked was that we keep it relatively small because I do not have unlimited chairs or dishes and I get overwhelmed easily with a ton of people crammed into my living room. So the plan was dad, my siblings, their partners and kids, and my grandma. We set the date, shared menu ideas, I started buying decorations and making lists like a nerd.

For context, my parents separation is still pretty fresh. They split officially 10 months ago after a long time of my dad having "friendships" that were obviously more than that. Mom finally had enough and moved into a condo. Dad has been hinting he is seeing someone but refused to give any details, said it was "too soon" for us to meet her and that he wanted us to "respect his privacy". Fine, his life. I was honestly relieved to just have a calm holiday where everyone could focus on food and kids instead of divorce drama. Then, about two weeks before the holiday, dad calls me and basically announces, not asks, that he will be bringing his new partner, "Lena". He adds that he expects everyone to be welcoming and that he does not want "any attitude" or "sulking kids". I said I was surprised because he had made a big deal about privacy and also that mom will be there, and it might be a lot for her to sit in my tiny living room with his new girlfriend like nothing happened. He cuts me off and says that he is tired of "walking on eggshells" around us, that he deserves happiness, and that if my mom "chooses to feel awkward that is her problem". Then he says something like, "If you are hosting, you host all of me, including my partner. If you cannot do that, I will remember it."

I told him I was not comfortable being the stage for his grand reveal, especially when he refused to even have a real conversation first. I suggested he either talk to mom and my siblings first or we keep this holiday as just immediate family and he introduces Lena another time. He doubled down, said I was being controlling and disrespectful, and repeated that he was bringing her and we all needed to accept it instantly. No compromise. After that call I just sat there shaking. I kept imagining my mom trying to make small talk while dad acts like a teenager with a new crush. The more I thought about it, the more I felt like I was being forced into choosing a side or pretending years of hurt never happened, inside my own home that I was supposed to feel safe in. So the next day I texted the family chat and said that I was cancelling hosting. I told them I loved them but I was not up for managing the tension and that maybe it was better if everyone did their own plans this year. My mom immediately called and said she understood completely and would just spend the day with a friend. My siblings were disappointed but mostly at our parents in general, not me.

My dad, on the other hand, absolutely lost it. He said I was punishing him for moving on, accused me of "siding with" my mom, and even hinted that I was being ungrateful because he helped with my college and with the down payment on my place years ago. He keeps texting that I have "ruined" the family holiday and that all I had to do was be polite to his partner for a few hours. One of my aunts chimed in that I should have just hosted anyway and "not made it about the divorce". I feel guilty because I know my siblings were looking forward to everyone being together and I did pull the plug, but at the same time I feel like my boundaries got bulldozed the moment dad turned my home into a test of loyalty.

TLDR: I offered to host our first big family holiday in my apartment. My dad demanded to bring his brand new partner and insisted we all accept her instantly, even though the divorce is still fresh and my mom would be there. He refused any compromise so I cancelled hosting completely. Now he says I ruined the holiday and am punishing him for moving on. AITJ?