No, NTA you said you and your family gave him a whole entire year to say something if he didn't want a cat in the same household.

It sounds like you and your brother need some therapy. He can get help for his fear of cats and you with how you're feeling. Can your cat stay with a family member for a while until you leave the house? If your brother does get some help, it would be good for him to be slowly introduced to the new kitty. Just need to take it one step at a time.

Yeet the brother.

If your brother's fear of cats is really that strong, he's overdue to seek professional help. But, unless he gets a real diagnosis from a real doctor, he cannot claim to have any phobia. Stop accepting self-diagnose from anyone, internet is not a substitute for years of real medical education.

I've just finished reading through the comments and I can now see where you getting the information that the brother "Agreed". I also read that the OP is a literal child and the brother is an even younger child. The little brother, who is terrified of cats seemed to think that he could 'get over it' if she bought him an axolotl. Children say all sorts of things to get what they want because they lack impulse control and an understanding of consequences. Which is why choices are (or should be) made by parents. Regardless of the little brother's capacity to agree to such an arrangement, she was willing to exploit his desire for a fish to get what she wanted regardless of his phobia. Clearly there are much bigger issues at play here than a cat. The OP is now threatening suicide and running away. The real AHoles in this situation are the parents, who clearly do not have this situation in hand and who should have properly made decisions for the welfare of both children. The brother needs therapy for his phobia and the OP needs therapy to help her develop resilience and self trust.

There is nothing on the post that suggests that he ever agreed to getting a cat or to suggest that he ever did anything indicate that he was ok with getting a cat, or that he remained silent and didn't speak up? I don't know where you have derived this information from - but it's not in the post.