The Dark Divine by Bree Despain
Description (Google Books):
Grace Divine, daughter of the local pastor, always knew something terrible happened the night Daniel Kalbi disappeared--the night she found her brother Jude collapsed on the porch, covered in blood--but she has no idea what a truly monstrous secret that night held.
The memories her family has tried to bury resurface when Daniel returns, three years later, and enrolls in Grace and Jude's high school. Despite promising Jude she'll stay away, Grace cannot deny her attraction to Daniel's shocking artistic abilities, his way of getting her to look at the world from new angles, and the strange, hungry, glint in his eyes.
The closer Grace gets to Daniel, the more she jeopardizes her life, as her actions stir resentment in Jude and drive him to embrace the ancient evil Daniel unleashed that horrific night. Grace must discover the truth behind the boys' dark secret...and the cure that can save the ones she loves. But she may have to lay down the ultimate sacrifice to do it--her soul.
Recommended by: Galleysmith
Special Notes: I've actually seen lots of talk about this book around the blogosphere, but the most recent post by Galleysmith finally made me add it to my Wish List!