irritated with Yamada-san's insecurities

She's 17. She is shy, socially awkward and has one confirmed friend. She's a virgin. Her girlfriend on the other hand is a beautiful and insanely popular athlete who (if you believe the rumors) has been going out with other girls before.

It would be flat out idiotic and bad writing if she wasn't insecure.

I'd suggest Kase-san walk away.

Because Yamada would be anxious about her first time? No offense, but I'm happy I never dated someone with such an astounding lack of empathy. There's love and there's barely tolerating someone's presence for the sake of sex and this sentiment sounds like the latter.