Owwww. Talk about depressing! Especially as I'd written an ending where they stayed together, but had then decided on an ending where they'd split up. She was right. Those were the two outcomes and a life doing something else like working on a supermarket checkout beckoned.
But I'm the sort of person that if you say 'can't' to, I become even more determined to do whatever it is. I therefore needed a third option. I thought for a bit - alien abduction? death? I couldn't think of an alternative to the stay married/separate choices.
Then the brainwave. What if the book ceased to be about the marriage? What if the book was about the woman's search for meaning and purpose in her life? She could do that whether she stayed married or got divorced. In other words, the bored publisher's comment became irrelevant. So I re-wrote with that in mind and Adultery for Beginners became, yes, a book about an affair, but that's not what it's really about.
I think - and of course it may be just me - that it's all too easy to fall into established patterns of thinking. The book events are about marriage, therefore the book is about marriage. But actually, it's usually about something else entirely, and as writers, it's our job to find the something else.