Wings of Starlight by Allison Saft

Brimming with magic and romance, a young fairy queen must form an unlikely alliance or risk an unspeakable danger destroying all she holds dear in this fantasy adventure from New York Times bestselling author Allison Saft.

It’s been centuries since a warm-season fairy in Pixie Hollow has crossed into the Winter Woods, and while most fear the legends of monsters lurking in the frozen lands, Clarion, can’t help being intrigued by Winter’s stoic beauty. But under the watchful eyes of the current monarch and the court’s seasonal ministers, Clarion has little time to dwell on daydreams while the days to her coronation dwindle away.
That is, until reports of a monster crossing from Winter into Spring make their way to the palace. Clarion sees defeating this threat as an opportunity to prove that she is worthy of her new role. But instead of finding a monster at the edge of Winter, she finds Milori, a young guardian of the Winter Woods. Together, they form an unlikely bond as they race to save their lands.
But as their alliance warms to something more, they will discover there is a reason a warm-season fairy and a winter fairy must not be together. And the cost could be just as deadly as the monsters that prowl the Winter Woods.