This has been great. They're super close to the point of confronting each other and having the needed talk.
As for Mitsuki: I'm not sure how much she was aware of. They were both deliberately paying attention to other things and Aya is with friends. They're all with friends really, it's a small gathering so she might not have really noticed until the end there. There's not much danger though given it's essentially a family gathering and they're adults. She just leaned her head, not anything too crazy yet.
We stopped mid-moment so that makes the pause more impactful for dramatic effect but Mitsuki will likely react after this if she understands what's been happening. She might not know as much as the reader but we'll see. It could just look like Aya leaned on another girl, if Mitsuki hasn't noticed what was going on over there. That would explain the shocked face better. Should be interesting next chapter!
It seemed pretty pointed that Aya was sneaking glances at Mitsuki the whole time, and every time Mitsuki was very pointedly
not looking her way.
She even comments on it, wishing Mitsuki would just look at her--and she finally does, just in time to see Aya rest her head on another woman's shoulder.
Which sorta would lead to Aya confirming that she's the only one in love/putting effort into their relationship, in her eyes, I expect.
That said, we do let off halfway through the moment, so no telling what Mitsuki's reaction will be outside of her dropping her drink in surprise.
Though Rinko being right next to her and
also seeing it, when she knows that Mitsuki & Aya are dating and quite close, makes me think there's more in the tank before a conversation happens and we move toward the resolution phase.