Divine Blood by Beck Michaels

The Shadow demon nearly took everything from Dyna, and it would soon return for more. When she discovers a way to fight back, she must go on a perilous journey and risk it all for those she holds dear.
Along the way, she meets Cassiel, a Celestial Prince with magic blood and wings as black as his heart. He wants nothing to do with Dyna until he learns she could lead him to a place he has been searching for all his life.
But reaching their destination is not as easy as they thought, nor are they the only ones searching for it. With danger at every turn and harrowing secrets between them, the quest will require much more than determination. They must fight for what they desire—or die trying.