Turret by Camille Peters

Princess Gemma has been trapped for years within a magical turret, a fate she deems fitting for a sickly princess with little purpose. The enchanted walls offer security, which she’d do anything to maintain, for though she knows she should want to escape, her prison seems far safer than the outside world. But the magic of the tower has begun to fade, bringing with it not only unpredictable dangers but the very real possibility that soon Gemma will be forced to leave the prison she’s grown to trust.
The tower’s shifting magic isn’t the only thing changing, for the longer Gemma spends with her faithful guard, Quinn, the more she realizes that her feelings for him are inappropriate for one of her royal status. But the deeper her feelings for her guard grow, the more Gemma yearns not only to escape the tower in order to see more of the world beyond, but to break through the walls she’s built around herself.
But even if she finds the courage to fight for the life she wants—one filled with possibilities far more beautiful than she’s ever allowed herself to imagine—there’s one final obstacle for her to overcome…for she’s not the only who has created walls. Though she’s striving to lower hers in order to allow her guard in, Quinn is determined to protect her from his devastating secret by keeping her out.