Then why don't you stop reading? This series apparently doesn't meet the expectations of a lot of the people that continue to read each new translated chapter as soon as it comes out. Tanking the ratings out of spite and filling these threads with NTR complaints is a waste of time. I don't see the point in continuing to read something that you feel no attachment to, you have no obligation to the author nor the series. None of you try to bullshit out of this saying "Oh I like reading trash". No one looks smart proudly proclaiming that they eat garbage.
If that isn't you then I genuinely don't see why you're having trouble seeing what's going on with the story. Both parts of the story have been told in "first person" to limit our view of what's going on. For Hikari's arc, she was oblivious (and the reader by proxy) to what was going on with Yuu despite being right next door, ultimately blindsided by her best friend kissing her crush. She fell in love with him "lately", but he's been there all this time, outside of her notice. For Aya's arc, she can't even be honest inside of her own head. It's similar to how flippant she was in Hikari's arc, but she seemed to have mellowed in the future. She was going to prostitute herself before she even had her first time. She was flunking out of a prestigious high school because she wasn't showing up to classes. She pretended to be a grown woman, but it only showed how childish she was. Her backstory under normal circumstances would be sympathetic, but she acts in incredibly unsympathetic ways. Given her nickname is Yami, I don't think her classmates have a high opinion of her either. This chapter is her trying to stay with the guy she just spilled her heart out to, but portraying it, at first, as if he's the one losing out. The way the story is progressing, she probably learns to be more honest with Yuu, though I'm guessing that ends in one more bout of childishness. I'm mostly certain she is intentionally unsympathetic (for now), given how she narrates in this arc, presented coming off the cliffhanger that still isn't resolved. This is also an extension of the stuff Hikari doesn't know, still outside of the time she started noticing Yuu. With this the reader will know how the current Yuu came to be, even though Hikari won't.
The missing part in all of this is Yuu. Despite everyone saying he's in love with Hikari, we haven't actually heard it directly from him. Despite being in both arcs, what we know from him was mostly filtered through Hikari and Aya. I don't think there's gonna be a straight answer for now. The focus right now is Aya, and if people don't want to buy into her that's fine. But if you keep reading despite that, you find something good about this, even if you don't want to admit it earnestly.