I swear Ayano and Miyoshi are the "save the best for last" couple.
Yep or they just are both afraid of rejection by the other right now due to how less common same sex relationships are.
I get the impression that Miyoshi hasn't realized her feelings for Ayano. Ayano is clearly into Miyoshi, but Miyoshi just thinks they're close friends. I doubt they're worried about stigma. Everybody in their class seems aware of Chie and Ai and seems fine with it. More likely Miyoshi hasn't realized how Ayano feels and Ayano is afraid to push the issue, probably because she's worried Miyoshi is straight.
It's getting to the point it seems like it'd be hard for Miyoshi to still be oblivious, but it does seem that it's being scripted that way. I guess to make a bigger impact when realization finally does occur? I mean, Miyoshi figured out that Ayano kissed her on the lips for crying out loud! Still, it's all good!