I have many feelings about this “mini-arc.”
My understanding of Yamada’s problem was that Ichi wasn’t spending much time with her, and she was angry because he spent time with Moe when he could have spent time with his girlfriend. Ichi realized that Yamada was sad but that he had ignored her, and he felt he shouldn’t have.
I’m very sad that the first thing he thought was to call himself “trash,” when he didn’t do anything wrong. The only time (shown to us) he broke his study routine was to visit a friend. Was it the right choice not to visit Moeko? Was he supposed to ignore all his other relationships because Yamada exists? Is he supposed to always prioritize her in every single instance?
But I also don’t want to place any blame on Yamada. She’s a teenager in her first relationship, heavily spoiled, and her boyfriend — who she hasn’t spent much time with recently — was visiting his friend’s house instead of studying like he told her he would. Sadness and anger are to be expected.
The “resolution” (in quotes because this issue could resurface) felt a bit incomplete to me, but the most important thing is that they came to an understanding, even if I don’t fully agree with it.
Really, the missing piece for a healthy resolution (at least in my eyes) would be Ichi realizing he isn’t a “pile of trash” for not being with his girlfriend 24/7, and Yamada realizing that she can feel sad even if it's not rational to expect someone’s undivided attention.
However, a healthy resolution doesn’t mean a more interesting one, and this conflict resurfacing later is an interesting plotline. Given the quality of this manga, I trust Norio’s choices.
In the end, I liked it. It made me think a lot, which is a good sign. I hope for more sweet and wholesome moments in the future, though.