Bridgerton Book 6. When He Was Wicked. Julia Quinn

Everything was much simpler... when he was debauched. And then Michael Stirling, London's most scandalous ladies' man, fell in love so quickly and recklessly that he could barely stand on his feet. He fell in love at first sight at a dinner on the occasion of the upcoming wedding of the Earl of Kilmartin, his cousin, and Francesca Bridgerton - HER wedding. In 36 hours, Michael lost Francesca forever. Years passed. Now Michael is the Earl of Kilmartin, and Francesca is free. But for her he is still just a close friend and long-time confidant. Until one dangerous night, when his "girlfriend" innocently finds herself in his arms, and passion beats even the most secret sins...