Romantic relationships are characterized by several paradoxes and can be understood as one of the biggest dilemmas that human beings must deal with. Romantic relationships ambiguities can be broadly found in the theme of fidelity and infidelity. This study aims to investigate the way young single adults conceive and experience fidelity in their romantic relationships. To this end, we interviewed five heterosexual men and women. The subjects of the study were middle class single college students living in Rio de Janeiro, between the ages of 18 and 25. Qualitative method and semi-structured interview (Bardin, 2011) were used. We found that the subjects conceive romantic relationships in the present as superficial, temporary, empty, and trivial. They also consider fidelity a pivotal trait in any relationship and expect fidelity from their partners. One is perceived to be faithful when he/she is transparent and sincere, and when pre-established agreements with the partner are met. Some subjects highlight that they are unfaithful to themselves, and many have difficulties in establishing boundaries between fidelity and infidelity. It was concluded that, despite the many social transformations, fidelity remains a key aspect of romantic relationships, and young people expect their partners to be faithful. Being faithful means not only maintain sexual exclusivity, as well as transparency, honest and sincerity with partner.