Narcissism is known to be related to romantic success in short-term contexts (dating, early stage relationships) but also to problems in long-term committed relationships. We propose that these diverging romantic outcomes of narcissism can be explained by differential associations with agentic versus antagonistic dimensions of grandiose narcissism: Narcissistic Admiration and Rivalry. Both dimensions serve the central narcissistic goal of gaining and maintaining a grandiose self-view, but do so by different processes: Admiration is characterized by the tendency to promote the positivity of one's self-view by seeking social admiration (assertive self-enhancement). Rivalry is characterized by the tendency to protect oneself from a negative self-view by derogating others (antagonistic self-protection). Across 7 studies (total N = 3,560) using diverse measures and methodological approaches (self-, peer, and partner reports, as well as interpersonal perception measures in video-based studies, face-to-face laboratory encounters, and online surveys), we show that the short-term romantic appeal associated with narcissism is primarily attributable to the dimension of Admiration, whereas the long-term romantic problems associated with narcissism are primarily attributable to the dimension of Rivalry. These results highlight the utility of a 2-dimensional reconceptualization of grandiose narcissism for explaining its heterogeneous romantic outcomes. The findings further underscore the idea that different facets of personality traits might impact different aspects of romantic relationship quality, depending on the stage of the relationship. Such a more nuanced view increases the predictive validity of personality traits in social relationship research.