Prince of the Sorrows by Kellen Graves

Without an academic endorsement to make him valuable to the high fey, Saffron will be sent back through the veil to the human world. The place he was traded from as a changeling-baby, and a place he is terrified of. And while getting an endorsement shouldn’t be impossible, it’s hindered by the fact his literacy is self-taught, using books stolen off of Morrígan Academy’s campus of high fey students.
When mistaken identity leads to Saffron learning the true name of brooding, self-centered, high fey Prince Cylvan, what begins as a risk of losing his life (or his tongue) becomes an opportunity to earn the future he wants. In exchange for an endorsement, he and Cylvan form a geis where Saffron agrees to find a spell to strip power from Cylvan’s true name. While Prince Cylvan doesn’t know Saffron can barely read, Saffron is determined to meet his end of the deal in order to remain in Alfidel—or, maybe, just to remain by Cylvan’s side, as affections grow stronger every night they spend alone in the library together.
But as other human servants soon fall victim to a beast known only as “the wolf”, Saffron realizes he has embroiled himself in a manipulative reach for power like he never anticipated—and even Prince Cylvan cannot be trusted. Between the wolf, uncovering forbidden magic, and his growing feelings for the prince, Saffron will have to decide which is most important to him—his endorsement, the lives of his friends, or the prince’s life and wellbeing.