Romantic Passion Over Time: The Roles of Self-Expansion and Sexual Desire in Long-Term Relationships

Abstract Maintaining romantic passion is a central challenge in established relationships, yet comparatively little is known about the relational and motivational processes associated with its persistence. This cross-sectional study examined whether self-expansion, sexual desire, and relationship duration were associated with romantic passion among 205 German-speaking adults in relationships lasting at least two years. Twelve supplementary semi-structured interviews contextualized participants’ experiences of romantic intensity. Self-expansion was positively associated with romantic passion, r = .445, p < .001, as was dyadic sexual desire, r = .413, p < .001. A statistically significant indirect association between self-expansion and romantic passion through sexual desire emerged, b = 0.161, 95% bootstrap CI [0.068, 0.308]. Relationship duration was negatively associated with romantic passion, r = − .382, p < .001. Contrary to expectations, however, relationship duration strengthened rather than weakened the positive association between sexual desire and romantic passion, b = 0.014, p = .023. In a multiple regression model, self-expansion remained the strongest unique correlate of romantic passion, and the model explained 31% of its variance. These findings highlight self-expansion and sexual desire as relevant relational processes associated with romantic passion in established relationships, while underscoring the need for longitudinal and dyadic research.