These two have been pretty chummy with each other for a while now, especially when Akizuki hurt his leg. I believe some of the times they hang out with each other are off screen and their interactions were not made to be as prevalent as the main couple.
I feel that the author tried to make the couples distinct, the main one is more lovey lovey, while these two are more “chill friends”.
Now, as to whether things are rushed, perhaps that is the case. The publisher won’t allow the author to make 1 1/2 volumes worth of chapters so some probably end up getting cut/not produced to fill not more than one volume.