I didn't really need the chapter explaining how depression works, but for completeness' sake it's a very good thing. Not super fond of the phrasing of "your depressive" either, as that feels very depersonalizing to me and if Sheffield wanted us to avoid conflating our loved one with their illness, that seems like questionable wording.
That said, this was the book that made it clear to me it's okay for me to feel unfulfilled, unappreciated, and utterly exhausted by relationships in which I'm reduced to a caregiver. Being a caregiver can mean being nothing more than a part of someone else's recovery, someone else's care plan, someone else's life.
Is it any wonder that so many of us end up in a wildly asymmetrical and sometimes even codependent relationship with someone who legitimately does need us and is legitimately unable to reciprocate on an equal level? Is it any wonder that so many of us end up neglecting our own needs? It's what we're taught to do, with perhaps one throwaway line about taking care of ourselves before returning to the (apparent) real point of our existence.
This book was very validating for me as someone who has struggled and continues to struggle with being reduced in that way. Just knowing that I am not some uniquely-selfish callous narcissist, that I am in fact responding in a sensible and ordinary way, meant a great deal. I didn't get a lot of coping tools from the book, I got that at the accompanying message board that Sheffield started before her passing, but this was a necessary piece of me accepting that my dissatisfaction did not make me a bad person... just a person.