Forlorn. The Forlorn Series, #1

Bad luck seems to follow Grace Fortune wherever she goes. She was orphaned at a young age, and her musical talent got her accepted to a prestigious school for the arts, where she was caught in the middle of horrific school shooting that nearly takes her life. But then she meets gorgeous loner, Jared Lorn, and falls madly in love. There is only one problem. Jared is not exactly human. He's a Nephilim, an angel/human hybrid, descended from a cursed line of fallen angels known as the Watchers.
Having a half-demon boyfriend who's under a curse from God can be tough enough. But then Grace decides that she wants to help free Jared from the curse by killing his angel father, Azazel, who is bound up in the Abyss, where he will be judged at the End of Days. She has a powerful ally in her guardian angel Ariel, who has given her a weapon: a Song that can tame demons. With a crew of loyal friends, Grace and Jared will travel to the ends of the earth, battling the forces of heaven and hell that seek to defeat them.
Yet as their love grows stronger, they will find themselves in danger of succumbing to the very corruption that caused the Watchers' downfall.