Duke of Dalliance by Shannon Gilmore

A sweet love story…
Marry a quiet one, and you won’t need a mistress…

Arlington Fox, the Duke of Dallimain, had a decade-long reputation for stealing other men’s mistresses. The ton called him the Duke of Dalliance. He wasn’t especially proud of the label, and if the real truth were told, he’d only stolen one mistress who just happened to belong to his father. She also happened to be his governess. Rumor traveled fast, and his misdemeanor had turned into a full-blown legend by the time he was twenty. Nine years later, his reputation is being put to good use, helping a wallflower teach a much-deserved lesson to a breed of catty women born into meanness.
A warning to the wise: There is a limit to what a wallflower will tolerate.