You're correct about the first kiss, but the main issue remains unchanged. Even that kiss from Eri followed a significant buildup centered on how her two friends were concealing things and acting on her throughout the manga, leaving her constantly scrambling. At that point, because she'd been kept in the dark, she ended up stumbling into things while trying to wrap her head around these sudden changes and keep Fuyuki close to her. Then Fuyuki, understanding what happened, added on to the issue with her sudden second kiss days later.
Firstly it wasn't days later, but literally
the next morning. They talk about 'last night.' It wasn't Eri's fault that she stumbled into it, at all - in her head Fuyuki was dating Kisaki, she
made Fuyuki into a cheater, while thinking that Kisaki was the person that Fuyuki really loved. Its not her fault that it happened, and there was no way she would have forseen it coming (since she lacks foresight often) but it was absolutely not random or delayed.
And I also think Eri is straight, hence why I am interested to see what she does in the next chapter, in terms of what she's willing/prepared to do if she intends to try and keep Fuyuki innher life like I suspect is her overall aim.
As an aside about the "Eri is straight" conversation, using this comment as the jumper just because it was the first one that I saw, like half of the point of her story is that after turning down a girl she saw a friend and the reaction to her she never once turned down anyone until 'the last one' before Kyou [Chp 1, 4, 5], and she just straight up says that she never even loved them from the start, only to "fall in love later" [Chp 4] which while a generally decent representation of how most people fall in love, feels more like it was done on purpose for storytelling and pushing hints. It's likely she never loved them
at all [all the way through to even the current chapter its been obvious she had no romantic feelings towards kyou]
. She seems highly detached from every relationship in her life, romantic or otherwise, except for specifically fuyuki.
Like she doesn't just have
one childhood friend, does she? Everyone - even herself - points out that she puts way too much stock in 'platonic childhood friends' [Chp14/15 is the big one, but its repeated throughout] but, like, does she? She wasn't getting broken up with because there 'was another guy she was always hanging around' and Kyou himself says he confessed, in part, because he felt like she didn't appreciate him as much as she did to Fuyuki [Chp 14.] Its not that she puts too much stock into friendship, or the concept of childhood friends. It's
specifically about Fuyuki. It's
always been specifically about Fuyuki. No one else has ever, or
will ever take up more space in her mind palace than specifically Fuyuki.
Is that to say there's romantic feelings there? Not really, but stamping "straight" onto her forehead and calling it a day feels similarly incorrect. She's likely closer to aro/ace spectrum and saying yes to guys because that's just 'what she's supposed to do.' having sex with them because 'that's what she's supposed to do.' and so on, always ending up seperating with them because she prioritizes Fuyuki - the thing 'that's not what she's supposed to do.' but she won't budge on it.
Sexuality in general is far more complex than gay, straight, and throwing 'homoromantic, biromantic, heteroromantic' alone isn't enough to scratch the surface. Everything up to this point has pointed to Eri, in particular's, sexuality to simply be "more complicated than that" rather than just slamming a label on her.