My Lord Beast by Anna Volk
Blurb: Celeste is a low born serf working in her Lord’s Castle. She is physically and mentally abused by her Lord’s aunts. She dreams only of living peacefully with Sebastian, Lord of Castle Kilskeagh. He rules his Clan with honor but can never be happy, as his love for Celeste can never be returned. His passion flares brightly but with it comes the Beast, for he is cursed to never find true love. The three witches of Kilskeagh have made sure that the bloodline will die with Sebastian, for each time that he feels pleasure, he is cursed to turn into a Beast.