Lilith

He fell in love with a demon. But Will is not entirely human himself.
Will was a sheltered, home schooled boy from Kansas when he finally follows his dream to be a photographer in New York. Success soon follows as he gets his dream job at a newspaper, but a relationship eludes him. When he is sent on assignment with the most beautiful woman he's ever met. Will seems to intrigue Lily and she soon admits she's in love with him.

Wedded bliss follows, then everything changes when Lily gets a phone call. He knows when she says she has to go out of town, she's not coming back. He has questions for her about what happened when she snuck out the bedroom the night before. The truth ends up stranger than fiction. Lily is really Lilith, the very first demon. Will is also not human himself, but a Nephilim. His father was a fallen Grigori angel who has escaped the pit of hell. War is brewing between heaven and hell and somehow, Will is at the center of it

From sheltered home schooled boy to Heaven's weapon, Will is not prepared for any of this