EDIT: This was meant as a reply to a now-deleted post asking to try and explain why the characters feel so distant now.
I tried to in my posts over the last few pages. From how I see it, Konatsu is frustrated with herself for wanting to act against Koyuki's best interest and to keep the exclusive connection (initially based on their shared loneliness) she used to have with her and her only, despite the fact that it was Konatsu herself who pushed her towards opening up to other people. And she's also frustrated with Koyuki for not understanding where she's coming from since Koyuki thinks that other people will fill the void that her going away will leave inside Konatsu; it won't, and Konatsu's current feelings are telling her that only Koyuki's presence and attention can ease her loneliness.
As for Koyuki, she just seems to genuinely be incapable of analyzing the situation deeply enough due to her lack of social awareness and experience. She outright can't understand that Konatsu considers their connection special and that she'd think of her differently from how she'd think of any other friend she might make. This was evident from very early on, for instance when she told Konatsu there was no particular reason why she called out to her on the day she first came to school despite Konatsu wanting to hear her say she also considered their first meeting special.
If I had to fault one of the two over the other, it would have to be Konatsu. She's the one with the ability to start to try and sort things out by being straightforward, although she won't because she knows she's in the wrong.
The thing about Koyuki and Konatsu is that they are basically both introverts. I think we need to keep the role of Kaede, the extrovert, in mind in all of this, too. (Why are they all "K" names?) While it's true that Konatsu pushed Koyuki to open up, she sees Kaede as the one who actually got Koyuki to open up. She knows this is a good thing, but she also feels guilty or inadequate that she wasn't able to give Koyuki the kind of support she needed to open up. Konatsu has a bit of a sense of inferiority toward Kaede or unworthiness toward Koyuki at this point. She wanted to see herself as the frog, but now sees herself more as the salamander. And, since she never knew the "old" Koyuki, she can't appreciate her own role as the bridge that got others to first see Koyuki as someone who could be approached. Without Konatsu, it is doubtful that Kaede (or others) would ever have spoken to Koyuki.
Couldn't agree more with your point on lack of social awareness/experience. Not something that's going to get cured overnight, though. And a lot of these observations are things that are easier to see from the outside.
