Us by David Nicholls

I loved this book!  Here's Kirkus Review:

In his picaresque fourth novel, Nicholls (One Day, 2010, etc.) artfully unveils 25 years of a couple's relationship.
Shortly before Douglas Petersen, his wife, Connie, and their 17-year-old son, Albie, are to take a “Grand Tour” of Europe, Connie makes a surprising announcement: She thinks their marriage “has run its course” and is thinking about leaving. Connie is panicked at the thought of Albie going to college at the end of summer, leaving her and Douglas alone in the house. Douglas, a straight-laced biochemist who “had skipped youth and leapt into middle age,” came along at a time when Connie, artistic and free-spirited but directionless, needed someone sensible. Despite the announcement, Connie still wants to take this holiday together, and as their journey begins, so does Douglas’ examination of his marriage. Part travelogue, part personal history, Douglas’ first-person narration intersperses humorous observations of their travels, during which Douglas usually finds himself out of step with his art-loving wife and son, with his wistful recounting of their back story, from his unlikely courtship to his recent positioning as a misfit in his family of three. After a ruinous morning in Amsterdam, when Albie unwisely confronts a trio of arms dealers and Douglas intervenes in a way that infuriates his family, Albie runs away, and the “Grand Tour,” deemed a failure, comes to an end. Yet before it’s too late, Douglas seizes a chance to find his son, win back the affections of his wife, and make this journey, both literal and figurative, a heroic one after all. Nicholls is a master of the braided narrative, weaving the past and present to create an intricate whole, one that is at times deceptively light and unexpectedly devastating. Though the narration is self-conscious at first, it gradually settles into a voice that is wistful, wry, bewildered and incisive, drawing a portrait of a man who has been out of his league for a long time.
Evocative of its European locales—London, Paris, Amsterdam, Venice, Madrid—and awkward family vacations everywhere, this is a funny and moving novel perfect for a long journey.