The fact that Dear Debbie’s primary narrators, Debbie and Cooper Mullen, are married and lying to each other reflects the novel’s thematic interest in the danger of secrecy in romantic relationships. Debbie keeps a number of secrets, such as the dangerous contents of her garden, the revenge plots she enacts over the course of the novel, and the fact that she was sexually assaulted in college. Cooper has one major secret: His decades-long struggle with alcohol dependency, which he has kept secret from Debbie since before their marriage. Debbie and Cooper Mullen’s relationship history suggests that secrets breed more secrets and that secrets can become more dangerous over time.

Both Debbie and Cooper are aware that the other is keeping a secret, and the novel suggests that this knowledge breeds even more secrecy in their relationship. Debbie justifies not telling Cooper about her sexual assault by pointing out the fact that “he’s got secrets too. Plenty of them” (201). She repeats this idea later after drugging Zane, demanding to know, “[W]hy should I tell the truth when he’s been lying to my face?” (213). These passages suggest that Debbie believes that her lies are warranted because Cooper is already lying to her.

Cooper echoes this logic by attributing his secrecy to the fact that “it feels like she’s keeping something from me” (122). Although he admits that it’s reasonable to “blame it on the secrets I’ve kept from her” (122), Cooper insists that “everything I’ve done recently is because of the distance” (122) caused by Debbie’s secrecy. Like Debbie, Cooper believes that his partner’s secrecy justifies him in keeping more secrets, suggesting that secrets breed more secrets.

Debbie and Cooper’s relationship also suggests that secrets become more dangerous over time. Debbie explains, “after we were married, I was scared to tell [Cooper about the sexual assault] because I thought he’d be mad at me for not telling him sooner” (201). Cooper repeats this argument in his justification for not telling Debbie about his alcohol dependency: “[A]fter we were married, I realized it was too late, and she would be furious with me for lying to her” (285). The near-identical structure of these arguments suggests that this is a foundational issue in their relationship. For both Debbie and Cooper, the amount of time they had been keeping the secret adds to the danger and pain of the secret itself.

In the novel’s Epilogue, Debbie and Cooper begin the process of healing from their decades of secrecy. Debbie tells Cooper about her assault, while Cooper reveals his alcohol dependency and his ongoing treatment. Both partners respond with compassion and understanding, suggesting that their fears were groundless. In reestablishing honesty and transparency in their marriage, Debbie and Cooper seek to move forward with healthier communication styles.