Background: previous studies indicate that being in a relationship has a beneficial effect on the physical and mental health and also significantly affects the quality of life. One of the essential elements of the relationship is intimacy, which includes sharing experiences, support and mutual understanding, as well as respect and care for the good of the partner. Being in a relationship, the nature of this relationship (marriage vs. informal relationship) as well as the level of intimacy and the assessment of the quality of the relationship may be in relation to the personal sense of well-being. In this research we intended to estimate the significance of these variables for the sense of well-being and analyze which of these variables have the same meaning for the sense of well-being of young women and men. Participants and procedure: the sample consisted of 431 people (217 women and 214 men) aged 23 to 37 years (46% of the study group were people in relationships, and 54% were single). Results: the conducted research confirmed the relationship between the sense of eudaimonic well-being and having a partner, as well as the relationship between sense of intimacy with the partner and the assessment of the quality of the relationship, indicating some differences in this respect between women and men. Conclusions: it seems that an important issue, worth investigating in our research, concerns the reasons why individuals live a single life (voluntary and involuntary singles), and whether or not they are satisfied with this kind of life. Just as in the case of relationships it is not only the fact of being in a relationship that makes a difference but the level of satisfaction with the relationship as well, also in the case of singles satisfaction (or dissatisfaction) with living alone may prove to be significant.