Reread The End of the Affair. It's depressing, all the religious explorations are slightly boring, and the main male character is a jerk, but it inspired my to a fanfic project.
I retrace the conversation in my head, in as much detail as I can manage, trying to work out how we'd got from there (Molly's dental appointment) to here (imminent divorce) in three minutes. Ten, anyway. Which turns into an endless, three-in-the-morning brood about how we'd got from there (meeting at a college dance in 1976) to here (imminent divorce) in twenty-four years.