Ok, while i know that my one opinion isn't going to settle a whole debate, here's my take on this
Miki unknowingly, and seemingly unwillingly, grew romantic or semi-romantic feelings for Aki due to the comfort she gave her at the time of her breakup and vulnerability. After mot realizing these feelings when they sprouted and grew, when she finds out that Aki and Shiho are now dating, but after spiraling and sorting through her feelings she realizes that she might've fallen in love with her sister and is reasonably distraught over this causing another layer of denial and overall frustrated feelings that she is experiencing at the moment. It also seems that she is dealing with the fact that she is now assuming herself a bad person because of these unwanted feelings and the way she is acting because of the realization of these feelings, which again ties into the current hard, and possibly vulnerable, state of mind that she is in right now.
I want to end this... tangent(?) off by stating that admittedly i do and have read some incest manga or other literature before and i don't entirely have a problem with it as long as it doesn't affect me, if that makes any sense? But while reading this chapter i just didn't get the vibe that this is going to end up being incest, just that it is diving into Miki's emotional vulnerability, so for those angry about this seemingly incestuous subplot, i may be wrong but i don't expect it to last for all that long.
"Kind of reminds me of the internal conflict from "My Sister's Best Friend, My Lover" but without the Kiku character equivalent to help sort things out so far." - stated by DJNebulous 24/6/24 2:51 pm
i agree with this, i get the same sort of vibe from this as i did in that, but i don't think it's quite the same. but yeah, the angry, vulnerable sort of internal though sequence gave me this sort of vibe.