The Killer Who Kept Me by Davidson King

Nothing about Em’s life is simple. He’s treated worse than anyone in the house, punished for every minor infraction, and has zero chance of ever escaping his current situation. He dreams that someday he’ll be free of this nightmare and finally find someone who will want to keep him.
That dream may come true sooner than he thinks.
Saros Tancredi is the most dangerous and powerful man in all of Eastbury. The loyalty he has to his family is unparalleled to anything else. When he wants something, he gets it. He rarely worries and lives without fear. All of that changes one night when he’s faced with his own mortality. When it seems like it will all end, out of nowhere, a stranger jumps in and saves his life.
Saros and Em live separate lives in the underworld. Saros is the most compelling man Em has ever known. Em is the savior Saros never knew he needed. When secrets long buried emerge in the midst of a current war, they threaten to tear away any chance the two men have of finding a happy life together.
One thing Saros and Em know for sure—they’re not going down without a fight.