Bound by Sin by Stevie J. Cole

This is how the Fallen came to be. This is how Gavin Hunter grew into the illusion of the man he is. The actions that would ultimately lead to the end of mankind were set in motion the day the Fallen gave into woman; creating a darkness that lurks in every crevice of the mortal world - and man has know idea of it. This is merely the beginning of a journey thousands of years in the making.