Married by Starfall

She will wed a fae sorcerer to save her mother's life. He will kill her on Starfall night to save himself.
Venya’s mother is dying—and Venya’s only remaining option is to bargain with a feared fae sorcerer, Kassimir the Dark, for a cure. She is desperate enough to do anything—or so she thinks, until Kassimir asks an impossible price.
Kass is no ordinary fae sorcerer. There's a demon bound to his heart, and the bonds are breaking. When they shatter on Starfall night, the demon will kill him—unless he can find a sacrifice to take his place. When a desperate elf maiden arrives upon his doorstep, an arranged marriage is the perfect ruse to keep her.
Venya finds Kass to be the opposite of the wicked necromancer she expected, and Kassimir cannot help but soften in the face of the shy elven librarian who unlocks his heart. Something forbidden and dangerous blooms between them—but the deadline of Starfall approaches, and Kassimir cannot evade the demon's lust for vengeance.
A terrible betrayal looms, and one is doomed to die on Starfall night unless fate itself can be defied by love.
Married By Starfall is a standalone enemies-to-lovers fantasy romance (guaranteed HEA and fade to black heat level) set in the existing Altarea world and featuring characters from the Chronicles of Pelenor and Darkness of the Living Forest series.
Married By Starfall is book six in the Arranged Marriages of the Fae series.