Do we actively maintain monogamous relationships by force of will, or does monogamy flow automatically? During functional magnetic resonance imaging (fMRI), male participants in a romantic relationship performed the Implicit Association Test (IAT) to evaluate implicit attitudes toward adultery and a go/no-go task to measure prefrontal activity implicated in explicit executive control. Subsequently, they were engaged in a date-rating task in which they rated how much they wanted to date unfamiliar females. We found that the individuals with higher prefrontal activity during go/no-go task could regulate the interest for dates with unattractive females; moreover, the individuals with both a stronger negative attitude toward adultery and higher prefrontal activity could regulate their interest for dates with attractive females, and such individuals tended to maintain longer romantic relationships with a particular partner. These results indicate that regulation of amorous temptation via monogamous relationship is affected by the combination of automatic and reflective processes.