The tension and disagreement really did feel like it was coming. Granted the presentation of kouhai was unexpected and how her presence incites this friction is unwelcome, I did feel that they would have an issue because of Mashiro's codependency issues and lack of confidence. We've been given hints to Mashiro's mental state, how lonely she is and how she craves Nagisa's time so I expected they'd have some sort of misunderstanding. I thought it would be presented in the way of Nagisa losing time for Mashiro causing her to retreat in the very manner she's doing now.
I do like that internal monologue of Mashiro's, how she realizes telling Nagaisa's worries wouldn't necessarily help things because she'd be imposing her feelings on Nagisa and would only succeed in shifting the burden onto Nagisa.
I feel more for Mashiro than I do Nagisa since it's strange that Nagisa would act so courteous to someone that insulted her girlfriend? Kouhai's involvement didn't seem necessary until now because I did not realize just how stunted Nagisa is? Did she honestly think it was okay to be so helpful to someone who actively hates her girlfriend and has belittled her girlfriend to both their faces???? I still don't like Kouhai and I feel like this could have been achieved if they just went with losing time because of cram school. Now we're getting to see how clueless and insensitive Nagisa is in contrast to how Mashiro's trying so hard to keep things together and be mature about this by putting Nagisa's feelings first.