We know what the author wanted to convey, which is that Kei believes her partner is emotionally unfaithful to her, and feels sad and lonely. You say over and over again that all the plot points are ambiguous but that's not the case. The details are ambiguous.
No, we don't know what the author wanted to convey, that's the whole point. You don't know, I don't know, because the story was muddled garbage. The plot is ambiguous. You don't know what is even happening during the events in the manga, for fucks sakes it goes from a random kiss to Sachi missing for three months to them fucking like bunnies, and you don't know how it ends.
For one, there are clues. We can look at Kei's hatred of tobacco smoke, and imagine she had a traumatic experience with a man who smoked tobacco threatening her relationship. We can look at Sachi going to the store to buy new headphones, and infer that she may be trying at a new start with Kei, unbeknownst to Kei. We can look at the last page of Kei smoking a cigarette and glaring into the pitch blackness, and infer that the relationship is ending or at least not going anywhere happy.
If your clues require their own ambiguous interpretation then they are not clues. They are just more bullshit you have to dig through to try to figure out what the hell is going on. Kei hates tobacco, we don't know why she hates it. We don't know how the headphones are connected to her ex-boyfriend, so her buying new ones doesn't have any meaning. Kei smoking while wearing Sachi's headphones doesn't mean anything, it's not a clue. It's a convoluted mess that means nothing. It's the yuri equivalent of throwing a bucket of paint against a canvas and trying to interpret meaning from it. We don't know why she is wearing the headphones, we don't know why she is even smoking. Also, she's not staring into pitch blackness, she is staring at the reader from the corner of her eye.
I don't love this manga by any means, but there's definitely an intention, a feeling conveyed. Details periphery to that intention being left to the imagination are NOT a sign of an inept writer.
When literally every detail is left up to imagination and interpretation then it's a sign of an inept writer. When two polar opposite interpretations are equally plausible then it's a sign that the writer is terrible at conveying whatever intention they had.
You seem angry at something if you don't like it you don't need to come here to attempt to silence the people who do enjoy creating theories and never being sure of anything.
