Social media provides a useful platform for people to share information, develop networks, and connect with each other online. While social media allows one to foster relationships with ease, it may pose challenges for individuals in a romantic relationship. Mounting evidence suggests that social media use may have an adverse impact on relationship dynamics, largely due to reduced time and attention for relationship partners. However, it remains unclear (1) how the increased use of social media may lead to negative consequences of relationship quality; (2) how the increased use of social media and negative relationship consequences together may trigger social media addiction; and (3) whether there are psychological factors that may contribute to the mitigation of the negative consequences. Here, we explored these issues by selecting Instagram (IG) as the target platform because the unique feature of tracking objective time of usage within the IG app allowed us to more accurately determine the length of IG usage. Using a structural equation modeling approach, we found that increased IG usage reduced relationship satisfaction, which led to an increase in both conflicts and negative outcomes. The sequential effects of reduced relationship satisfaction and increased conflicts then triggered addictive use of IG. In contrast, tendency to make sacrifice for the relationship partner in everyday life produced a positive effect on relationship satisfaction, which in turn reduced the likelihood of conflicts, negative outcomes, and addiction. Taken together, we have delineated pathways through which excessive social media use may detrimentally affect both relationship and personal well-being and identified sacrifice as a possible psychological factor to mitigate the detrimental effects. We believe that these findings add to our understanding of the processes by which social media influences romantic relationship and highlight the interactive effects of social media and relationship on causing unexpected, adverse consequences.