Nothing worse than being rejected by someone who doesn't even know they're rejecting you lol.
There is one thing that this makes me wonder, since Yamada is totally an innocent about sex does that mean when she saw Kase-san's naked breasts, she really was only self conscious about her size comparatively rather than being turned on by her girlfriend's body?
^^^^ I dunno I see it more as Yamada doesn't know what a love hotel is but she certainly knows what sexuality is. I still think she was self-conscious of the naked breasts as being, as you put it, turned on. It's not like you learn love hotels and sex at the same exact time. Take it from someone who was overly innocent and sheltered for a bit of his life...I knew about sex and was conscious of things of this sort long before I knew that things like vibrators, or even masturbation, was a thing, just an example.
So I wouldn't read too much into it. Just Yamada being adorable and naive, and needing some room to grow as an adult. But on her own time, with maybe some coaxing at most from Kase.