I couldn't stand the stress, at first, of being the sole family caregiver in my mother's case, but our doctor's secretary said to me, "Why should you be spared?" I recognized the truth and wisdom in that. Indeed, why should I be spared? And, from then, I had the strength and felt it was an honor. Although, as you say, it's horrific to see your beloved in a deteriorated condition. At least, we can witness with them while they go through the valley.
Bless you for being there for your Mom!