I recently had the pleasure of hearing the author do a presentation on her work. She explained that for her, writing novels is a way of exploring questions about the human condition.
If asked most could provide a definition of love, but when in a relationship it is a more complex thing incorporating who we are or think we are, and who the other is or who we think the other is.
Contemporary psychology teaches that there are many limits to self understanding. I have come to think of love as a special kind of friendship.
Her description of the couple loosing the sense of the boundary between their bodies while in bed seems to be part of it. Still aging brings ceertain stubornneses and personality quirks to the fore so in some ways our sense of self as unique increases.
Part of love must be allowing an other to be who they are - accepting them as they are - perhaps that is what the couple is acheiving as the novel ends.
The author mentioned that she wrote several different endings for the book.
The ending she used has a bit of the lady and the tiger to it. The reader doesn’t know what will happen to the couple - do they have quantum entanglement.
For me the test of a good story is do the charactrers become real to my mind. I would say that is true in this book. The author also says one of the reasons she writes is that she likes beautiful sentences - a good foundation for any book.