A Touch of Darkness (Book1 of Accepting Darkness)

Kiera White, a fifteen-year-old girl whose reality is tormented by dreams and darkness, cannot discern between what is real and what is not. She is faced with horrific monsters in both her nightmares and the shadows of her waking world. Her father, determined to keep her safe from those who wish her harm, has concealed her existence from Ri'elle, another world. However, a single mistake reveals their whereabouts to the most dangerous man alive, Dexer Cain. (The Webtoon has the same name and is published under the same author.)