On the other hand that is also one of those things that annoys me about romance culture, the whole notion of your girlfriend/boyfriend/wife/husband being "stolen" by someone else as if your partner was just a passive object instead of being the actual person in the cheating who made promises to you (which might or might not include sexual exclusivity depending on mutually agreed upon preferences between everyone in the relationship) and should keep those promises or break up with you no matter what any third person tempts them with.