My central point is that the story is bringing too much attention to two facts: a.) that she's cute, b.) that he's not touching her, despite finding her cute.
I'm a bit confused...is this all going back to the discussion with his brother saying he first let her stay because her face was cute? Your read on this is one point of view for sure but there are tons of ways you can take that line and their relationship, and a lot of outcomes folks can hope for, for more reasons than being into the taboo.
Plot-wise the characters already acknowledged their complicated relationship and settled into something familial+ for now in the dialogue they've spoken themselves. Like yeah, folks tend to be a little bit more kind if they find someone cute or charming. He feels bad about it but it wasn't like the others. I don't think he brought her back just for sex even while drunk and I don't think he super wants it right now, though it may change. they're just Aware of each other.
To me, the story is about the complexities of love, (and again, this could be friendly, familial, romantic, sexual), between strangers in the shadow of a traumatic background, and how clumsy even adults can be. Sayu and Asami are kids who need support, but they're pretty mature and getting more so by the chapter, aware of their position in the world, the dangers they can be in, and doing their best to help and survive. Contrasted by Yoshida who really didn't think about what he was getting into as he still dealt with his own difficulties with relationships after the breakup in HS, the brother's struggles to connect with and support Sayu, her mother's emotional abandonment, and the awkward games of cat and mouse that just end up backfiring for Yoshida's senpai and kouhai.
Are you sure you should be reading this anyway? Like the title and premise alone are a big "will he or won't he?" indicator. There's going to be comments and questions from characters and fans on his feelings about her and their romantic potential.
To have something where it's never brought in question in a story in a modern setting, especially considering Sayu's history thus far with the men she's stayed with, would be way more unrealistic and rose-tinted. It's brought up a lot because people are worried. They feel the alternative for Sayu is deperate and scary but they don't want to just leave her with Yoshida if he could be taking advantage of her. And even though they're friends with or in love with him, they still reasonably question his motives and concern themselves with the potential that love and desire can change forms over time.
If the thought that it could swing romantic is that upsetting it may not be a good idea to engage with this sort of manga.
I'll also say the stolkholmed reader comment is very condescending. Between the tags and premise people would generally know what they're getting into, and would typically read it because they're interested in the outcome, however it swings. Yes, various types of endings can be more important to some based on their personal feelings, interests, or experiences, but lashing out at or belittling folks who may want something different isn't standard or okay.
That bit about insulting an entire culture too... Japan absolutely does not have the monopoly on fucked up culture on what I assume you're saying is the subject of romance for underage persons. We're conflating the real world and an author's story here, but I will address both: I've yet to run into a real world society without a problem, and the various countries in the west are not only not the most progressive all around, they aren't the standard to which all other places should ve held on every subject. Concerning kids for instance, even the U.S., as loud as dialogue is concerning their development and well being, still allows child marriage and makes divorce for them hard. And there is pushback on getting these things outlawed.
You can have your thoughts on how different places handle real issues, and I encourage you to fight the good fight in the right place, but to judge group of people for fictional stories you're seeking out that aren't even exclusive to them? It's certainly not all of their literature, not even everyone there is into it, just like elsewhere, and it is not The Problem.
Also, forbidden love is a genre encompassing a multitude of relationship-types. Social status, age, wealth, culture, etc all come into play. It's not "normalizing" anything if it's classified as forbidden...? And for this story, if it were normal in this setting no character would be worried about MC or the girl at all.
We'll see how it plays out, but at the very least it's good that Sayu found the support she needed to try going back home, and nearly all of Yoshida's other love interest got some emotional development of their own.