The Baroness of Sin by Ava MacAdams

One naughty little meeting can’t hurt…

Lady Martha Worter will never forgive her late husband for scarring her soul beyond repair. Now determined to get her lost life back and experience desire, provoking her handsome but proper neighbor becomes her favorite pastime.
Living a predesigned life, James Williams, the Earl of Barristen, thought he could control everything, but for three exceptions: his wife’s death, his seductive neighbor’s games, and the profound enjoyment her mischief brings him.
Tempted to become more than just friends through their illicit agreement, their fear of commitment is not the only thing knocking on their door. For an awfully familiar figure would rather see them both broken than happy together.