The present study investigated the disclosed marital infidelity of Iranian middle-aged men using the Strauss and Corbin systematic approach. We sought to analyze the reasons, contexts, mediators, strategies, and consequences of marital infidelity in middle-aged men. The research field was middle-aged men with marital infidelity experience who had referred to Mashhad counseling centers in the first six months of 1403. The qualitative research method was based on the Strauss and Corbin systematic approach. 11 interviews were analyzed with the aim of achieving a conceptual model of marital infidelity. In the qualitative explanation and conceptual model, we sought a deeper understanding of the dimensions of marital infidelity and the factors that lead to this behavior in middle-aged men. The results of the study showed that feelings of emotional failure, monotony in marital relationships, and midlife crisis are among the key factors in marital infidelity in middle-aged men. The conceptual model showed attention to social and cultural influences on marital infidelity behaviors of middle-aged men. This study not only identified the reasons for marital infidelity, but also attempted to examine its consequences on family and social relationships. The results indicate that each of these stages should be considered in the intervention process