Halo Bound — Eden Hudson

The holy champion chosen to save the world is enslaved to a sadistic fallen angel and losing the battle for his sanity.
The guy chosen to save the holy champion is his binge-drinking redneck brother.
So, basically, the world is screwed.
Meet the Whitney boys:
Colt-a mentally unstable holy soldier with a rapidly deteriorating hold on reality. His last plan to rid the world of evil either failed horribly or went off without a hitch. With the constant torture and brainwashing, it's getting hard to be sure of anything but the sick attachment he's developing to his beautiful tormentor.
Tough-a smart-mouthed honky-tonk hero trying to drown his problems in music, women, and good times. He hasn't spoken to Colt in five years-not since their disagreement over a nymphomaniac vampire turned into a drunken slugfest-but they're still brothers. Tough knows he can't leave Colt fighting for his life and his sanity alone. The question is whether Tough can fight off his personal demons long enough to save Colt from the literal ones.
"Halo Bound is the first book in the Redneck Apocalypse series."