The purpose of this study was to examine how social networking site (SNS) use, specifically Twitter use, influences negative interpersonal relationship outcomes. This study specifically examined the mediational effect of Twitter-related conflict on the relationship between active Twitter use and negative relationship outcomes, and how this mechanism may be contingent on the length of the romantic relationship. A total of 581 Twitter users aged 18 to 67 years (Mage=29, SDage=8.9) completed an online survey questionnaire. Moderation-mediation regression analyses using bootstrapping methods indicated that Twitter-related conflict mediated the relationship between active Twitter use and negative relationship outcomes. The length of the romantic relationship, however, did not moderate the indirect effect on the relationship between active Twitter use and negative relationship outcomes. The results from this study suggest that active Twitter use leads to greater amounts of Twitter-related conflict among romantic partners, which in turn leads to infidelity, breakup, and divorce. This indirect effect is not contingent on the length of the romantic relationship. The current study adds to the growing body of literature investigating SNS use and romantic relationship outcomes.