Only a few studies have longitudinally explored to whom emerging adults prefer to turn to seek closeness, comfort, and security (called "attachment preferences"), and previous studies on attachment preferences in emerging adults have focused only on the beginning of romantic relationships but not on the end of relationships. Czech emerging adults (M = 21.47; SD = 1.48) completed the questionnaire of attachment preferences at two time points, Wave 1 (Summer 2013) and Wave 2 (Summer 2014). Latent difference score analyses revealed that emerging adults who were not in a romantic relationship in Wave 1 but started a romantic relationship between the two waves (n = 97) and those who had a romantic partner in both waves (n = 379) were both more likely to increase their attachment preference for the romantic partner and decrease their preference for friends, whereas those who did not start a relationship (n = 185) were not. Emerging adults who were in a romantic relationship in Wave 1 but were not in Wave 2 (n = 69) decreased their preference for the partner and increased their preference for friends. In all the groups, attachment preferences for the mother, for the father, or for the family did not change. Multiple regression analyses further revealed that for those who had a romantic partner in both waves, their length of romantic relationship was associated with changes in attachment preferences for romantic partners and for friends.