Demon Bound by Nina K. Westra

After years spent isolated in a lonely castle with her cruel husband, Raiya will do anything to escape… even make a deal with a demon.

When Raiya’s husband imprisons a monster from the hells, she sees an opportunity to free herself and spite her husband at the same time.
It’s said that demons are immensely powerful, halfway between mortals and gods. If Raiya can use her knowledge of rune magic to break the demon’s binding, he might agree to protect her from her husband while they escape together. That is, if he doesn’t decide to kill and consume her, instead.
The demon only requires one thing in exchange—her body.
Demons live off the fear and lust of mortals, which means that she’ll have to find a way to sustain him during their journey.
There’s only one thing more terrifying than sleeping with a demon: falling in love with one.