Dear Mr. Fairbanks by Alyssa Clarke

Lady Persephone Blagrove owns a secret tendre for Mr. Richard Fairbanks, a man society has labeled a rogue. Often unnoticed and called a wallflower by the ton, she dares to break the bounds of propriety by writing an anonymous letter to him, sparking correspondences that lead to passionate and scandalous encounters.
Despite knowing Mr. Fairbanks is a gentleman determined never to marry, Persephone finds herself increasingly drawn to him. Every wicked encounter is a gamble of the highest stakes, which may leave her in ruined shambles with a shattered heart.