Devil in Ruin by Trisha Wolfe

Dominic:
Brianna Cassatto is off-limits. From the moment our families formed an alliance through marriage, she became untouchable. To not only me—but every man. I made sure of that by threatening all who dares to look her way.
In the dark underworld of mafia monsters and villains, there is nothing more dangerous than the desire for a woman you cannot have. That temptation can drive a man mad, make him do the unthinkable.
And when Bria is promised to my enemy, the beast within goes feral, far beyond the mere unthinkable.
I’m a devil with a stolen birthright, ready to reclaim my legacy and empire. With the atrocities I’ve vowed to commit, I’ll be on my way to hell.
And I’m taking sweet Bria with me.

Brianna:
For two years, I’ve waited for Dominic Erasto to see me as more than an unwanted stepsister, a burden, even an obstacle to his crown. He thinks of me as a spoiled mafia princess just waiting to be married off to the highest bidder.
But when that day arrives, no peace will be bought with my hand—not when the devil himself declares war. His spoils:
Me.
But I’m no wilting flower. Raised in a ruthless world, I will draw blood as quickly as he deems to steal it. And when the devil comes to take me, I will be hisruin.