All right, even trimmed down this is probably too long a post, but this is my guess as to what's going on with Ayako and where all this is going.
So, in this chapter, Ayako thinks that "in the end, wanting to be a family with someone was just a long dream from the very beginning." We also learn that she never knew her mother, and in the first half of this chapter we saw that she was probably molested as a child. (There was some debate over it here, but I can't interpret that panel any other way.) In that same section, we also learn that she doesn't understand her own emotions. We learn in earlier chapters that she was seen as emotionless by others. She says to Asuka when Asuka first confesses that "it's probably all my fault." And then there's Akira's line about how "that you-know-what of yours proved to be effective even on your own flesh and blood", which I think is a very important line that we still don't know the exact meaning of. I think these are all connected, and that there's something here which I think is going to be at the core of how the story develops from here.
My best guess at it is this: Ayako likely had a horrific childhood, though we don't know the details of it other than that she was molested and that she never knew her mother. As a result, she's deeply traumatized and has probably always perceived herself as broken. Akira's line about "that-you-know-what of yours" seems potentially also very revealing in this context. I am guessing that Ayako may have felt herself unable to truly love another person or to forge a connection on any level other than the sexual one, and I suspect she may have had a hypersexual phase at one point as a product of her own past trauma and her attempt to pursue some level of connection that she felt like she couldn't achieve otherwise. (This part is more speculative, but the "that you-know-what of yours" line makes me think there's something like that going on.) Once she had Asuka, that changed, but she probably still feared or felt that on the deepest level, she wasn't capable of love. Atsushi and whatever happened with him likely ties in with all this, but I still don't feel like there's enough information to say how, or what that relationship was like. Ayako does seem to view him in a basically positive light, for whatever that's worth.
Finding out that Asuka was sexually attracted to her probably was, to Ayako, a confirmation of some of her worst fears. To her, it was proof that Asuka had been influenced by her own damaged nature, and that there wasn't any way that she (Ayako) could love or be loved other than in the erotic sense. At the same time, she clearly feels attraction to Asuka and has before Asuka's confession (the flashback scene with the 'delicious' bento), which she suppresses and likely, to the extent she even allows herself to acknowledge it, views as the product of her own damage. (It probably is, honestly.) This grows all the more intense as Asuka escalates things, and then, this chapter, the dam breaks and she snaps into... basically, an old, hypersexual pattern, if my theory is correct. When she comes back to herself and recognizes what's happened, she basically feels it to be confirmation that she can only truly connect with others on the sexual level, and that things would inevitably end up this way. So she goes to Akira (who I think is an important figure to Ayako in ways that still haven't been revealed), and that's where we are now. That's my best guess, anyway... we'll see how things develop.
