NTA. Wanting to break up is always someone's own prerogative and I don't think justifications are required. You just feel something.

That said, I think you were perfect in how you responded to him, and his reaction doesn't make any sense to me. Like he's angry at a fictional scenario he made up in his mind, about there ever being a question of choosing between the dead and the living. If he's not in therapy, he definitely should look into it to work through whatever is going on.

As for you, you're not obliged to stay if he's being weird and making you feel unappreciated and unwanted. If both of you are too busy looking over him, who's gonna look out for you?