In recent decades, psychology delves more and more bravely into the socially most important and long-term mental phenomena, i.e. sentiments. Following the study of partnership or romantic love the issue of serious psychological study is jealousy in partnerships. The most essential issue is the role of jealousy in loving relationships, which is interpreted in various ways in popular and scientific literature. Since these relationships are studied more often on undergaduates’ samples, different research data seem contradictory, because young people have only a short-term and indefinite experience of partnerships. More long-term involvement in a romantic partnership could verify the hypothesis on the link between jealousy and love, which appears to clarify the role of jealousy in partnership not only in early adulthood, but also in middle adulthood. Both sentiments could be connected with such an important aspect of partners’ satisfaction as sexual satisfaction. The results of this research show a positive link between love and jealousy for 35–45 year-old males, but not for women, which revealed significant gender differences of the role of jealousy in long-term partnerships. At the same time, jealousy and love are positively connected with sexual satisfaction for both genders, but these links appear to be stronger for males. The data obtained have applied significance for family and couple counsel and psychotherapy, but many other factors should be studied and controlled at that, including the duration and the type of partnership, partners’ age, equality and symmetry in relationships, expectations, social tolerance, personal investments, own or adopted children, etc.