Infidelity is a widespread phenomenon across different cultures. Yet, not all people are unfaithful to their partners, and the current study aims to identify the reasons that motivate individuals to hold back from cheating. For this purpose, we developed an evolutionary theoretical framework which could enable a better understanding of the ultimate reasons that motivate people not to cheat on their partners. Furthermore, using a combination of qualitative research methods, we have identified 47 proximate reasons that could prevent people from cheating. By using quantitative research methods in a sample of 576 Greek-speaking participants, we classified these reasons in eight broad factors and two broader domains. One domain reflected considerations about the potential costs of cheating, and the other, considerations about the benefits of the current relationship. Women indicated a higher propensity not to cheat than men, especially if they were satisfied with their relationship, and because they would feel guilty. We also found that, the higher participants scored in conscientiousness the lower their propensity to cheat was, while the higher participants scored in openness the higher their propensity to cheat was.