Bound to the Fae Assassin by Tasha Black

Her magic is outlawed, and his love for her is forbidden.

Farrow must repress her magic for fear of the King’s wrath. But she secretly bakes balms for the villagers’ pain into the rustic breads at her parents’ bakery. When she happens upon a Fae Prince in disguise on the edge of the wall between worlds, he ends up obligated to her.
Blackthorn’s curiosity about the pretty mortal straying close to the wall ruins his mission and places him under a debt of obligation to the green-eyed temptress. Under her power, he travels home with her to save her friend’s life. And once he learns what Farrow really is, he is determined to stay a little longer and help her harness her magic. The only challenge is resisting the sizzling attraction between them. After centuries of boredom, he finds that Farrow excites something in him even beyond his desperate need to claim her.
But Blackthorn has his own reasons for being on her side of the wall. And ultimately Farrow may be the one to pay the price for letting his magic in.