A Lady, Her Lord, & Their Duke by Nicola Davidson

Dominant Lady Arabella Carlisle and her submissive husband Lord Neville Carlisle enjoy a rare ton marriage; a blissful arrangement of affection, discipline, no children, and the occasional gentleman lover with an unbreakable rule: threesomes are anonymous, one-night-only amusement at a club, not forever.
But on their tenth anniversary they match with a novice submissive, unmasked as Edmund Vane, Duke of Stanforth, a powerful yet coldly reclusive widower. Beneath his icy shell lies a wounded soul desperate to be owned, and Arabella and Neville can’t resist his aching need…or their own fierce desires. Soon they sink into a decadent world of dark pleasures, but as walls come down and feelings grow, the fledgling trio risks more. For rebellion always comes with a reckoning…

This fem domme Regency FMM romance contains explicit sex scenes, language, and enthusiastically consensual discipline.
CW: family member deaths