My dear Conni, you have every sympathy I can send. Yes, it's really hard. The bonk is real. You're not a hard or unfeeling person. You've just found your limits.
I had the benefit of hearing the phenomenon of compassion fatigue before I experienced it, so I had some sense of what was happening. If you do a Google-Scholar search on the term you'll find lots of scholarly articles on the subject, but nearly all of them study healthcare workers or caregivers in some capacity. It was used of nurses during the worst of the Covid surges. Relatively little that I have seen addresses the familial or communal experience of giving and giving until suddenly you're bone dry and you don't want to be. That's what seemed so inexplicable to me about this experience: I wanted to be more compassionate and caring, but I was just bone-dry, and it happened pretty quickly.
Again, please accept my assurances that you are not without empathy or care. I'm certain of that. I've read your work. No one who feels as deeply as you do is without compassion, but the bonk can come for us all.
All the love in the world, my friend.