Introduction <p>It is now well-established that the COVID- 19 pandemic had profound mental health impacts that were not distributed equally throughout all portions of the US population. In this study, we used mental health and COVID stress data from the National Couples’ Health and Time (NCHAT) study to test the differential impact of COVID stress on key indicators of mental health (e.g., depression, anxiety) among sexually diverse couples.</p> Methods <p>We leveraged a sample of <i>N</i> = 1515 couples (3030 individuals) from the NCHAT study, who filled out self-report measures of COVID stress (e.g., concerns about acquiring COVID, immunocompromised household members), depression, anxiety, general stress, emotion regulation, and positive/negative coping behaviors in 2020 and 2021. These data were submitted to a series of constrained latent variable actor-partner interdependence models.</p> Results <p>COVID stress had widespread impacts on mental health problems for groups identifying as gay/lesbian, straight, and plurisexual. However, people identifying as plurisexual (e.g., bisexual, pansexual) and their partners tended to experience: (1) a stronger COVID stress-anxiety association compared to people identifying as gay/lesbian and straight and (2) tended to be more dissimilar with their partners on mental health.</p> Conclusions <p>These results imply unique impacts of COVID stress among subgroups of people identifying as plurisexual and their partners, as well as prevention approaches for further study.</p> Policy Implications <p>Our study suggests that reliance on one’s romantic partner may be key to incorporate in future public health messaging yet may not be as beneficially impactful for all groups (e.g., people identifying as plurisexuals).</p>