Today, social networking services (SNS) function as emotional outlets for relieving negative emotional states such as stress, loneliness, boredom, and anxiety. As these negative emotions may serve as key triggers for excessive engagement, it is necessary to investigate the psychological mechanisms behind such behavior. This study adopts the I-PACE model as a theoretical framework and examines how four types of perceived negative emotional states—perceived emotional suppression, boredom, loneliness, and anxiety—lead to excessive use of SNS through immediate gratification and emotional relief responses. Data collected from a sample of 304 SNS users were analyzed using Partial Least Squares Structural Equation Modeling (PLS-SEM) to verify the causal structure among variables, and Fuzzy-set Qualitative Comparative Analysis (fsQCA) was employed to explore how different configurations of psychological conditions contribute to excessive SNS use. The results of PLS-SEM confirmed that, except for emotional suppression, all psychological factors significantly influenced emotional responses, and both immediate gratification and emotional relief were positively associated with excessive SNS use. The fsQCA analysis identified four distinct causal configurations, from which two underlying psychological mechanisms were inductively derived. These findings are expected to inform the design of interventions that foster effective emotion regulation and strengthen social bonding, thereby helping mitigate excessive SNS use.