Another hard to find great old book, with a much younger gorgeous wife married to an aristocratic, rich older man that started out adoring her and ended up a frail invalid from suffering a stroke after catching her in an indiscretion with a younger man, that's where the tale really starts, and what happens following that makes for a fascinating story right to the end. (Amazon)
Marie Adelaide Elizabeth Rayner Lowndes, née Belloc (5 August 1868 – 14 November 1947), was a prolific English novelist. Active from 1898 until her death, she had a literary reputation for combining exciting incidents with psychological interest. (Wikipedia)