AITAH for breaking up with my boyfriend and kicking him out because he wanted to let my younger brother go into the foster system?

I (26f) recently lost my dad. He had a 15 year old son, my half brother Parker. No one in my family wants to take him due to the fact that he’s my dad’s affair child, which he conceived during my late mom’s cancer treatment. Despite this, I love Parker dearly. Regardless of my dad’s massive assholery, Parker is my little brother.

I work in a lucrative field and own a nice condo which my (now ex) boyfriend Colin lived in with me rent free, he did contribute to utilities and other expenses though. We have the perfect home for Parker, and I can’t for the life of me think of a single reason that we couldn’t take him. When I brought it up with Colin, he said that she didn’t want to. I asked why, and he said that he just doesn’t feel like looking after a kid. I reminded him that Parker is 15 and won’t need constant attention or babysitting or anything like that, and Colin said that Parker would need “emotional attention” because he lost his father. I asked if he would really rather throw a fifteen year old kid into the foster system than deal with the emotional needs of said fifteen year old, and Colin said “yes” while looking a bit shameful.

I ended up giving him the ultimatum that Parker and I are a package deal, that I would be taking guardianship and that Parker would be moving in. I made it clear that the only choice Colin had was if he wanted to keep the relationship and stay in the house. He called me heartless for choosing my “cheating dad’s bastard son” over our five year relationship. I called him heartless for talking that way about a literal child, and he looked at me astonished and went to start packing.

I love my ex, I really do, but Parker comes first. He’s my own flesh and blood, the only brother I have, meanwhile there are plenty of other men out there. Still, my heart is breaking now that Colin’s moved out. I miss him, but I don’t regret my decision. Every time I think about what could have happened to my brother in foster care, I feel more love for my brother and less for Colin. My entire friend group has sided with Colin and pretty much ghosted me, which is what’s giving my pause here. Was I an asshole for what I did?