great flashback and it looks like Chiaki had some latent homophobia within her back when they were still in high school and re-reading the first chapter it really was still there lmao.
While Chiaki was clearly happy to be friends with a lesbian and even nonchalantly go to her lesbian bar. It also gives the impression that she's never actually taken a good look at herself and what she wants. Just in chapter 1 alone she talks about how romance just isn't for her because she never wanted to go all the way with a man, but then she also dismisses romance with a woman outright. To the point that Chiaki tells herself it doesn't count, when she's faced with the possibility that she had sex for the first time with a woman.
And it's not like she doesn't know gay people exist, because her best friend is the lesbian bar owner of the lesbian bar she frequents XD. So it really does just look like Chiaki has been carrying some internalized homophobia in part centered on the idea of wanting/needing children that allowed her to be friends with and have no problem with gay people in the abstract. But stopped her from admitting that she herself might be the same.