The purpose of this study was to investigate the influence of participant sex, sexual orientation, infidelity expectations, and love on emotional responses to emotional and sexual infidelity. Participants (72 lesbian women, 114 heterosexual women, 53 gay men, and 57 heterosexual men) completed a demographic form, continuous emotion ratings in response to hypothetical infidelity scenarios, the Infidelity Expectations Questionnaire (IEQ), and the Triangular Love Scale. Sex, sexual orientation, and commitment and intimacy among partners were significant predictors of various emotional responses to sexual and emotional infidelity. Alternatively, passion among partners and expectations about a partner's likelihood of committing infidelity were not significant predictors of emotional reactions to infidelity. Across participants, sexual infidelity elicited more distressing feelings than emotional infidelity. Group differences were also found, with women responding with stronger emotions to emotional and sexual infidelity than men, and heterosexuals rating emotional and sexual infidelity as more emotionally distressing than lesbian and gay individuals. Sex and sexual orientation differences emerged regarding the degree to which specific emotions were reported in response to sexual and emotional infidelity. Clinical implications are offered, including how mental health professionals might use these findings to help clients cope with the negative effects of infidelity on romantic relationships.