The Broken Circle, Book 1 of the Heraldy of the Fae Series

An ordinary teenage boy finds himself stuck in the middle of a magical feud that has raged on for thousands of years. Being born half-fairy, and yet raised as completely human, Blane Somerled must embark on a journey to bring balance back into the world, before the wickedness infecting the Winter Court finally destroys the Summer Knight for good.