Dreams of Darkness — Elizabeth K. Burton

Randrik alt Harbinnen isn't above seducing a reluctant woman, but he never thought he'd be doing it for his aunt. He didn't know that the forest-wandering race called the Drevnya drew their powers from sexual magic, nor that suppressing their emotions and sensuality could be fatal for them. But Perian, the Drevnya Adept raised by abusive human parents who tried to destroy her magical heritage, is more than he bargained for. Her dreams of a voice calling her from the darkness of the void lead both of them into danger they never imagined and a future they don't want. In the distant east, a towering evil has escaped imprisonment in the eternal void of the Everdark, and it is their destiny to seek it out and destroy it before it destroys their world.