In this chapter, we discuss romantic relationship maintenance in the context of self-expansion. Overall, we review the self-expansion model and its accompanying empirical literature over the past 30 years, and consider some implications and future directions. Specifically, we begin by conceptualizing relationship maintenance, describing the self-expansion model (including both of its key principles: motivation to expand one's abilities to accomplish goals and including close others in the self), and covering some of the foundational work conducted with couples (e.g., self–other overlap and relational benefits of shared exciting activities). We then review research showing that relationship maintenance and self-expansion are positively related, and discuss potential mechanisms and theoretical underpinnings. We next explore more recent research on individual self-expansion and its implications for the maintenance of close relationships. Throughout the chapter, we provide illustrative examples of how self-expansion is associated with relationship characteristics, behaviors, maintenance, and outcomes. These examples will hopefully allow readers to better understand the concepts, theories, and empirical findings, and also allow utilization of this knowledge in real-life applications. Finally, we end with a summary and discussion of future directions for self-expansion and relationship researchers.

The self-expansion model of love was developed in the 1980s (Aron & Aron, 1986; for a recent review, see Aron, Lewandowski, Mashek, & Aron, 2013). It emerged from an integration of two diverse worlds of knowledge. The first world of knowledge was relevant social-psychological theories of basic human motivation, and the little research that existed at the time on attraction and relationships. The second world of knowledge was from classical concepts of love.

The period when two people first fall in love often seems to be characterized by energized and intense emotions, preoccupation with each other and the relationship, and great optimism. Yet over time, as the partners get to know each other, there is a typical decline in this exhilaration, often even a sense of apathy and boredom, a reduced interest in each other and the relationship, and a less idealized vision of the future. Indeed, a typical decline in love and satisfaction after the initial relationship period is one of the most well-documented findings in the study of marriage in Western cultures (for example, Blood & Wolfe, 1960; Glenn, 1990; Locke & Wallace, 1959; Rollins & Feldman, 1970; Tucker & Aron, 1993).

However, there is considerable variation in the rate of this decline (Tucker & Aron, 1993). One longitudinal study that followed newlyweds for four years found that as many as 10% showed an increase in marital quality over this period (Karney & Bradbury, 1997). In addition, studies of individuals who have been married 30 years or longer have found small but significant numbers who report high levels of passionate love (Traupmann & Hatfield, 1981; Tucker & Aron, 1993), including high scores on Hatfield and Sprecher's (1986) Passionate Love Scale with items such as “I would rather be with ___ than anyone else.”