AITA for refusing to give up my dog after my sister's kid developed an allergy?

I’ve had my dog, Milo, for 5 years. He’s my best friend, and I adopted him during a really dark time in my life. He’s calm, great with people, and honestly better behaved than most humans.

Recently, my sister and her 6-year-old son moved in with me temporarily after she left a bad relationship. I didn’t hesitate — of course I said yes. Family is family.

But a week in, her son started developing a pretty severe allergic reaction. Turns out, he’s allergic to dogs. She immediately asked me to “rehome” Milo, saying it was “just temporary” and that my nephew’s health had to come first.

I told her no. I said I would help pay for air purifiers, keep Milo mostly in my room, vacuum daily — I’m doing everything I can. But rehoming my dog? That’s not an option. She called me selfish and said I’m “choosing a dog over her child.”

Now the whole family is split. My mom says I’m being heartless. My dad says it’s my house, my rules. Even some friends are saying “but it’s a kid, come on.”

I feel like I’m being emotionally blackmailed. Yes, it’s a kid, and I care — but this isn’t just a pet. This dog saved my life when no one else was around.

So… AITA?