The scientific community underlines that one of the main challenges for couples is the effect of time on sexual desire. Some studies suggest that although some dimensions associated with intimacy tend to increase during the relationship, sexual desire and the related constructs tend to decrease. Some researchers have recently suggested that couples' relationships with high degrees of sharing and fusion might be particularly detrimental for the sustenance of sexual desire. However, the authors found no empirical or theoretical studies that investigate the relations between intimacy and desire. Recovering the concept of differentiation as a possible influencing variable between intimacy and desire, this article develops reflections on this theme, which is of paramount relevance for the couple viability.