Wyn by Lily Mayne

I am a monster.
A ghoul. A demon. The bogeyman. I have been called all of them. Most creatures fear me, but humans are repulsed by me. They are terrified of me. They have created legends about me, ever since they became aware of my existence when the tear between our worlds grew and we—the monsters from their nightmares—flooded through in our droves.
There is only one human who isn’t afraid of me. The only one who matters. And I will destroy anyone who tries to hurt him or take him from me. Danny is mine.
For the first time in my unfathomably long life, I know what it means to want another so much that the thought of losing him threatens to ruin me. I will do anything to keep Danny with me for as long as I can have him—for as long as he is willing to stay by the side of an ancient, scarred creature with a voice so inhuman it has sent some mad.
For some reason, Danny loves my voice. For some reason, Danny loves me. And when we both decide that his natural human life is nowhere near enough time for us to have together, we go on a journey between worlds to the one place where we can do what it takes for us to be together forever.