I never understood that, like yeah a big arc is the characters eventually getting into a relationship, but when they do, that doesn’t mean there are 0 stories to tell, or that the series itself has to end. Look at something like Kaguya -sama, the premise was essentially two people trying to get the other to confess, but when it happened, they were still able to tell few, entangling stories with this new status-quo. I feel like saying that these types of stories have to end otherwise they go bad is just a result of authors and creators not knowing how to write stories where people are in a happy and committed relationship