Deep in Crimson (Return to Sanctuary) by Sarah Gilman
Kidnapped by humans and raised in a research facility, Jett was taught to believe his own race of demons insidious and violent. But a friendship with the archangel Raphael shatters Jett's reality. Caught between two worlds, his first months of freedom find him lingering on the fringes of his home colony, Sanctuary.
When the human who stole Jett captures another demon youth from Sanctuary, Jett learns of the real plan—to steal Raphael's archangel grandchildren. Jett wants to bring his captor to justice, but he must overcome the lies from his past and join forces with the demon Guardians, and the demon child's older sister, Lexine.
Irresistible attraction grows between Jett and Lexine, but Lexine's prophetic dreams of being mated to a poacher make her wary. And if Jett goes through the all-consuming process of becoming a Guardian, he may forfeit any chance they have of being together.