Savage by Sherrilyn Kenyon

From the moment he was born a god of light and darkness, Xevikan Daraxerxes was rejected by those who should have embraced him. A child of both realms, he was embraced by none. His is a lonely path that he’s walked for centuries as he’s done his best to avoid the divine politics of his parents.
But one can only stay neutral for so long. Now, Xev must face his past and learn from his mistakes. The world is in turmoil and his best friend and brother are facing enemies at every turn.
The evil he rejected is on the brink of destroying everything he knows and everyone he cares about. Either Xev embraces the savage inside himself that he’s spent centuries caging or he’ll be the last god ruling over a vacant, hollowed-out world.