That’s not how that works and you know that, Craig. When two people express intent to be in a mutually exclusive monogamous relationship, they’ve made an agreement with one another that they are a couple and therefore not single anymore, and any such behaviour would result in an end to the relationship. It’s not even remotely the same thing as going on a FIRST date with a girl and she’s texting other people. It’s not like she video called some guy, it’s literally the same thing as an incoming phone call or message, someone else made the action not her. You’re definitely allowed to have your preferences and if you want to only date people who also only date one person that’s great, have at it. But it’s ridiculously conceited to project your opinion on other people, especially when they’re behaving entirely regularly. When I was single and on first dates with women, I too would receive messages from other women I was speaking to or sleeping with. It’s societally normal to be talking with multiple people when meeting people in the hopes of finding a romantic partner. Once you find that connection, you stop talking to everyone else because you don’t need to anymore: you have found what you were looking for.