Yukaris situation isnt about bein gay, its about not recognizing shes in love cuz its a feeling she never had before.
Yukari is very straightforward. She repeatedly states that, in contrast to herself, "Tomoka has the
same sexuality as Ayu and is of her age" and therefore would be a better partner. Her issue is not
just about feeling love. Manga have an issue with women still being considered "straight" even under obviously gay situations. This is more of that.
That was the whole point of her thoughts last chapter, where she explained that despite their kisses, living together and relationship, she (Yukari) still does not "
share the same feelings in a fundamental sense," meaning her sexuality. She's questioning her sexuality and asking whether she's being authentic.
I think you're really missing what Yukari is saying. She genuinely thinks she's deceiving Ayu because she's not really of the same sexuality. Why do you think this is all spurring again as Tomoka comes out as gay? She heard Tomoka's speech about gay women and felt she didn't identify with Tomoka and the crying Ayu's experience.