The book that I have been reading is The Fallen by Thomas E. Sniegoski. It was two series in the book called the fallen and Leviathan.
On Aarons 18 birthday he begins to hear strange voices and is convinced he is going insane. But having moved from foster home to foster home, he doesn't know who he can trust anymore. He starts to have a crush on a girl at his new school however hes afraid she will think hes crazy as well.
Then a mysterious man begins to follow Aaron. He knows about Aarons troubled past and his new powers. And he has a message for Aaron, as the son of a mortal and an angel, Aaron has been chosen to redeem the fallen.
Aaron tries to dismiss the news and resists his supernatural abilities. But he must accept his newfound heritage. As the dark powers are gaining strength and are destroying him.