Fearbound: The Realms of Penumbria 1 by Claudia Peer

He's the nightmare she was warned about. But nightmares don't usually make your heart race. Beneath the Veil, Sinia's life was quiet. Safe. Predictable. Until the Veil broke-and safety with it. Now the world is crawling with demons and monsters, and her dream of living as a simple healer lies in ruins. Sent to uncover the Dark One's plans, Sinia stumbles into a destiny far greater than she ever wanted-and into the path of a man forged from secrets and shadow. To reclaim a broken throne, she must awaken ancient power and bind herself to the Lord of Fear himself. But oaths to darkness are never without cost. And when the heart of a monster begins to beat, Sinia must decide whether love can bridge the abyss between light and shadow...or shatter them both forever. Read more