Beast and Thorn - Chelsey Ann Tompkins

Reshina, Ravenfae Goddess, has relinquished her title of Cursebringer but has kept a select few of her powers. After using them to punish a man stealing from her people, she stumbles into the winter lands of Heartstone Castle. When a thorn from a frosted rosebush spills her blood onto the snow, an old curse she once delivered there awakens, dragging her into the Underrealm and binding her to its king.

Arthur, long since obsessed with Reshina after devouring the book she wrote years ago, roams the surface as a Beast and rules below as a haunted man. He offers her the only way to break the curse-drive a dagger through his heart. Refusing to take his life, she is drawn deeper into his grasp with every attempt to escape. The Beast marks her above the realm, and the man below soothes her wounds, taking her into his care. Caught between hunger and tenderness, Reshina must decide whether to break the curse... or surrender to the dangerous intimacy of the king who knows her far too well.