Wreaking Havoc by Grae Bryan

Sascha has always felt powerless, the weak baby of a cruel family. But that’s fine. He has his looks, his ample allowance, and a smattering of one-night stands to keep him busy. But when Sascha’s oldest brother offends the wrong people, Sascha finds himself in hiding with a target on his back. And when poking around in his temporary home leads to accidentally summoning the hottest demon Sascha could ever imagine, he has to ask himself: does he want to feel powerless anymore?
Kai has been waiting centuries for a summons. When he’s at long last brought to the human realm for his final contract, he expects to find another warrior hungry for battle and bloodshed. Instead, he finds himself bound to a saucy, scared mobster princeling who can’t stop looking at Kai like he’s dinner. It isn’t long before Kai decides that—for once—he wouldn’t mind staying exactly where he is, with a certain human for his mate.
But Sascha isn’t used to anyone sticking around, let alone caring for him in any real way. It’s up to Kai to convince Sascha he can give him so much more than protection. He just has to deal with those pesky enemies—and Sascha’s own meddling family—first.