Online relationship activities have been increasing sharply over the past few years. However, only a few attempts have been made so far to study users’ attitudes towards online relationships and infidelity. The present research used a questionnaire survey of college students to examine their attitudes towards online infidelity and behavior in online relationships. A cluster analysis was adopted to explore the differences among respondents in their attitude towards infidelity resulting from online relationship activities. Based on these attitudes, the respondents were divided into three groups: “conservative towards online relationships,” “accepting of non-sexual virtual relationships,” and “liberal towards online relationships.” This study found that females were more likely to rate online relationship activities, especially sexually related ones such as engaging in hot chat sessions and sexual relationships, as infidelity.