Many researchers have studied the factors that can contribute to a loving relationship remaining stable and having a good quality for both partners. Two of the most worrying concerns that people have in regard to love relationships are the jealousy and infidelity. The purpose of this study was to verify whether there is relationship between these two phenomena. In this study, 45 heterosexual couples with an average age of 24.6 years participated, who were recruited through an ad placed on the site of a public university located in the city of Sao Paulo. To assess the degrees of jealousy of the participants, “Escala de ciume romantico—ECR” was used. To evaluate the infidelity of the participants, the “Inventario de comportamentos relacionados a infidelidade” created specifically for this work was used. The results indicated that: 1) though it was so low, the jealousy is an agent of self-fulfilling prophecy for infidelity (r = 0.25, 90 df, p < 0.05); and 2) there is an association for the infidelity of each partner related to the infidelity of the other partner (r = 0.36, df 45, p < 0.05). These results indicate, therefore, that there is a direct relationship between the jealousy and infidelity.