Unleashing Mayhem by Grae Bryan

Matteo’s been running scared for so long he’s forgotten what it’s like to feel safe. Or maybe he never knew in the first place. Raised by a cruel man, tormented by an even crueler one, and recently rescued by a demon, Matty’s still jumping at shadows around every corner. When he sees a familiar face from the past and realizes his ghosts really have come back to haunt him, Matty does the only reasonable thing he can think of.
He summons someone even worse.
Nightmare is a solitary demon by nature. He’s never needed a companion or a lover or a friend, and he’s never minded being feared by others of his kind. But one taste of Matteo’s sweet, terrified soul and Nightmare needs more. When he’s finally summoned to Matteo’s side, Nightmare finds himself exactly where he wants to be. Now it’s only a matter of patience, seduction, and convincing his little human that one contract isn’t enough.
What they really need is an eternity.