Potential alternative partners can threaten the stability of established relationships, yet a romantic or sexual attraction to someone with whom you are not currently involved (i.e., a ‘crush’) appears common for those in relationships (Mullinax, Barnhart, Mark, & Herbenick, 2016). This study assessed prevalence of such crushes, individual and relationship predictors, and links to infidelity. Adults (N = 247, aged 25–45, 43.3% women) in romantic relationships completed surveys assessing individual characteristics (attention to alternatives, sociosexual orientation, attachment avoidance), relationship quality (satisfaction, commitment, intimacy), and infidelity. The degree of attention to alternatives predicted whether one had a crush on another while in a romantic relationship. Crushes were fairly common and seemed to have had few negative implications for those in established relationships. These findings will be of use to therapists addressing couples’ attraction to others.