Many of the relationships between the characters of A Curse So Dark and Lonely emphasize loyalty. Many of the driving motivations for the characters also concern loyalty to family or country. However, the novel shows that healthy loyalty requires a reciprocal relationship; if the parties involved are not on equal ground, loyalty may end up being a weakness. Through the development of the characters’ relationships, both with each other and with the groups they feel obligated to protect, the novel explores how loyalty can be both a help and hindrance.

Loyalty can bring benefits when both parties are able to act freely to protect one another. In the beginning, Harper views Rhen as the man who kidnapped her, and Rhen sees Harper merely as a prickly means to a necessary end, making them distrustful and wary of one another. Their loyalty to one another grows as they each open up about their troubles (Rhen’s curse and Harper’s home situation, respectively) and begin working together to address these problems. Their conversations involve honesty and boundary setting, with Harper in particular laying out guidance for how Rhen should discuss and respond to her cerebral palsy and Rhen respecting those guidelines.