Dreaming of Waterloo — Lynne Connolly

They called him “Lucky,” but he had hidden injuries nobody knew about. Plagued by headaches and living nightmares, Paul, Lord Sherstone returns from the field of Waterloo to London to find a wife he doesn't know and an estate he has to manage. He daren't let her close, even though he is falling in love with her all over again.
Married and abandoned in a month, Hetty learned to manage a large estate and fend off would-be lovers, but a threat emerges much closer to home and from an unexpected place. In need of help she turns to Paul but since his return he has only shut her out. Refusing to give up on the man she fell in love with five years ago, Hetty has to persuade her husband to let her into his bed -- and his heart.