Well, they do have a close to married relationship for a good while. Is true the label is for each to decide. Clearly they will be together in the future.
But isnt or will be the last time, even tho shes happy as is, that Sakurako shows she would rather have more. Is trick since she always in the series avoid to address the subject clearly. At the very least the "for now" still keeps some hope alive.
Personaly, i would be way happier if this fog dissipates. Still want to see they putting into words clearly. Mostly Kasumi. But i get the feeling as the progression went from the beggining that the author might get to that at the very end. Highly doubt we'll have them after the end of college as OL, tho i would definitely still read, so possibly the big good bye theme will be exactly they officially getting married as a reassurance that they'll always be together.