The Restless King by Danielle Berggren

A powerful young woman from Earth helping a sorcerer intent on the throne. A beguiling Fae king who has ruled for centuries…

Maeve Almeida has, for years, gone back and forth between her dull and traumatic life on Earth, and the fantastical world of the Realms where she can wield powerful magics. There she helps her friend, the sorcerer Sebastian Sekou, run the trials that will crown him as high king. All that remains is a duel to the death against Rodan, the Fae who currently sits on the throne at Realmsgate.
On the eve of the fated clash, Sebastian and Rodan unfurl their plans for Maeve, who is faced with life-altering decisions. What she chooses will ultimately shape the future of the Realms.