Recently, our daughter (17 in June) told my wife and me that she has started dating not 1, but 2 guys. No introductions needed since we already know them; they’ve been close friends of hers for quite some time now. Daughter put it as: why do I have to choose if I like them both and they don’t mind sharing?
I just don’t like it.
I don’t really see a problem with casual dating. She’s not committing to these people or lying about being committed. Alternatively, polyamory is a thing and many people live happily and fulfilled in that. None of these things are, in and of themselves, really problematic.