Social anxiety disorder (SAD) is associated with impairment in close relationship functioning, including romantic relationships. Although interpersonal theories point to dimensions of dominance and warmth as relevant factors, the momentary interpersonal dynamics that may be contributing to relationship problems remain poorly understood. In the present study, we examined contemporaneous and prospective associations between dominance and warmth in individuals with (n = 30) and without (n = 29) SAD and their romantic partners during a 10-min conflict task. Using the Continuous Assessment of Interpersonal Dynamics system and multilevel residual dynamic structural equation modeling, we found that on average, both partners tended to become colder and more dominant over time and showed strong warmth complementarity. Prospective effects indicated that momentary ratings of dominance and warmth positively predicted subsequent ratings, and cross-lagged effects suggested that each partner's behavior predicted change in the other over time. Critically, moderation analyses identified multiple cross-lagged effects that differed significantly as a function of primary participants' SAD diagnosis, all involving warmth. Our methods suggested that future work at longer time scales (i.e., across lags between 20 and 60 s) may be fruitful.