Glass Hearts by Lore Olesya

On the evening of her twenty-first birthday, Princess Maralena loses her freedom to a tournament victor—the dazzling but cruel Sun Prince. Torn from her home and thrusted into a kingdom of burning secrets, Maralena finds herself alone and at the mercy of courtly lies and dark ancient magick. In a realm where magick is a dwindling secret and bloodlines hold untold power, Maralena unravels her own hidden potential—one the prince will stop at nothing to control.
To both of their disdain, Mara’s only tether to hope becomes Evrardin, the brooding captain of the Sun Prince’s guard, sworn to obey the prince’s every command. Forced into uneasy proximity, Mara and Evrardin clash with sharp tongues, simmering glances, and touches that linger a little too long, their bickering hiding a tension neither dares to name.

As the prince’s sinister plans unfold and Mara’s power awakens, resisting each other becomes the most dangerous battle of all.