Cheating-a general term for extradyadic romantic or sexual behavior that violates expectations in a committed romantic relationship-is common and leads to a number of poor outcomes. Religion has historically influenced conceptions of romantic relationships, but societal attitudes about religion are in flux as many seek to retain spirituality even as affiliations with formal religion decrease. The present study evaluated a potential predictor of cheating that is more spiritual than formally religious, the "psychospiritual" concept of relationship sanctification (i.e., the idea that one's relationship itself is sacred). In a sample of college students in committed relationships (N = 716), we found that higher levels of self-reported relationship sanctification were associated with a lower likelihood of both physical and emotional cheating even when accounting for plausible alternate explanations (general religiosity, problematic alcohol use, and trait self-control). This association was mediated via permissive sexual attitudes; specifically, higher levels of sanctification were associated with less permissive sexual attitudes which, in turn, predicted a lower likelihood of emotional and physical cheating.