Who is Joan's Husband from A Year by the Sea: Thoughts of an Unfinished Woman and what is their importance?

Joan's husband is never named, which implies that, for this narrative, he is only a peripheral character, only defined by his relationship to Joan. This is the opposite of the way Joan had seen most of their marriage, since she always felt that her husband's needs were more important, while she tried to handle the role of wife and caretaker. Joan's husband only appears at the beginning and end of the book, and pops in a couple of other times, although he plays the important role of giving the story a logical end and beginning. Joan had spent so much of her adult life defining herself in terms of her husband, that her journey of self-discovery was bounded by her initial desire for separation, and her eventual resignation to starting over with a healthier relationship.