... Why does she have to have met him before? What does this add to the story? What, did she need some sort of serendipitous red string of fate connection of her own so that she doesn't lose to the other girl?
If she met him before like this, why isn't she more mindful of his boundaries in chapter 1? It read as endearing when we assumed she didn't know any better, but apparently she saw him whip out a bottle of disinfectant and go all germaphobe-wild on himself all the way back while they were in middle school and it just didn't register?
Please, please stop with the flashbacks. I can't remember a single instance of this manga where I thought the flashbacks added anything. All the romance was in the present. In fact, I strongly suspect you could cut every page with black space between the panels, including some full-length chapters, and lose nothing. Tsuzuri especially. She struggles so desperately to make her feelings known in the present it simply isn't necessary to show us her past directly. Her flashback chapters are all just rehashes of what even a mildly attentive reader already knew.
As for the flashback we just read... I'm no closer to an answer now than I was when I started writing this shit. Best I can tell the author is just stalling for time.