I've seen several stories or posts where someone finds out that the person they're dating is also dating multiple other people and they get upset about it, sometimes even ending the relationship or situationship/courtship altogether over it. And I notice a lot the responses to these stories are "well if you wanted exclusivity you should have asked for it".
But why is the onus on the person who wants a committed relationship? It's well known that a lot, maybe even most, people date with the intention of finding a serious and committed relationship, should it also be the onus of the person who is multi-dating to also clarify this and go "hey by the way I'm also seeing/dating other people?" I get that it may reasonably be implied on the first date, but after that? Why is the onus always on the one after something committed?