This is so sad. I didn't notice the tags, I was hoping things would get lighter. Like they're buying a present for Ucchi or preparing a surprise for her. That's probably what they're doing. Ucchi's self-doubts are hella relatable and it could work in canon too if Watamote decides to take a more serious route.
seems like it was based on something that could actually happen in the manga , ucchi starts to doubt miyazaki after she sees tomoko hugging her in the train and then miyazaki saying "kuroki-san ,he..." while ucchi is behind her hearing it.
I hope they dont bring ucchi more suffering in the manga and the thing about miyazaki become a chance for ucchi to finally admit what she feels for tomoko.