Back in 1961, after his wife died of cancer, C.S. Lewis recorded his anguish in a personal journal that was later published as "A Grief Observed". That slim book has been republished many times, is still part of the HarperCollins catalog (http://www.harpercollins.com/books/Grief-Observed-C-S-Lewis/?isbn=9780060652739), and continues to inspire and comfort many readers 50 years later.
The death of a spouse is a great loss, but there is a kind of grief that is as deep and yet more hidden. When someone's wife (or husband) leaves them, I believe that society does not have the same understanding or rituals for dealing with is as we do for death. In the middle of such grief myself, I wonder if my own journal may strike a chord with others in the same way that Lewis' book has. You can see the sort of content at http://www.unobservedgrief.com.
So, your opinion please ...
Imagine a book with a structure similar to "A Grief Observed", and with a similar balance between the personal and the universal, but reflecting the anguish of a person whose spouse has left them rather than died. Assuming the book could be well written, is it likely to be publishable? Is it likely to sell? Is it likely to help people who share the grief of divorce?
--Nat. 
I'm just going on what you've said before even looking at the book. Absolutely, it can be publishable, on the pure reasoning of so many people suffering from a spouse having left them. I have a handful of friends whom have been in this situation and it cuts deep into the heart and soul that it's wrenching.
I'm no professional in the writing industry, I only write and just by what you've shared above, with time and work and heart felt honesty, anything is possible and publishable.
And now I'll take a look at your book, as a layman writer