Sweet Vengeance by Viano Oniomoh

Joy needs a deal with a demon to bring an end to the man who'd ruined her life. Malachi needs a deal with a human so he can remain in the mortal realm, far from the sentries looking to drag him back to his sect in hell.

It's a match seemingly made in heaven. Except, Malachi doesn't expect Joy's thirst for vengeance to taste so sweet, and Joy doesn't expect a freaking demon to revive everything in her she'd thought long-dead.

After the deal is struck, and their contract had some to an end, they both realise that one contract will not nearly be enough.