Oooor, they're both teenagers with zero experience at romantic relationships and need to mature more. I don't believe Nagisa is consciously being this way, it's also unclear if she understands the implications of the things being said here. She didn't buy or accept her bs when the junior directly confronted her last chapter, and even reassured Mashiro.
We have the insight into all characters' thoughts and feelings, but the characters do not. Her saying "The Nagisa I know wasn't like this. You're the cause" (I paraphrased) isn't an inherently bad statement, but we know that it's meant negatively, and Mashiro probably does as well since the junior was glaring at her. We don't even know if Nagisa saw that clearly, like at all, which would make sense on why she was confused at the end.
In Mashiro's case, she's mainly just insecure and clingy, and doesn't know it's okay (and encouraged) to express that in words to her partner, because she has zero experience.
I'd give it alike 2 more chapters to see if this is really beat-for-beat just for the cliché, or them genuinely bumbling through due to inexperience and the work acknowledges that.