Alexander's Bridge (version 2) by Willa Cather

Bartley Alexander is a construction engineer and world-renowned builder of bridges going through what's known today (but not in 1912) as a mid-life crisis. Although married to his wife Winifred, Bartley resumes his acquaintance with a former lover, Hilda Burgoyne, in London. The affair proves to gnaw at Bartley's sense of propriety and honor. (Summary by Wikipedia)