So what signals do you think this text is clearly sending about what outcomes in terms of plot or character are in the category of “probable/highly likely”?
I cannot predict an outcome, but I can at least sieve out unlikely scenarios. There is of course nothing speaking against the possibility that after severe shock (perhaps of a stressful confrontation with Reiichi + his ex) Kaoru might break down mentally in unexpected ways...
As I've repeatedly said, I can't really see a happy ending for this story, but I can at least say that this story has not been awfully going off the rails. Most of the conflict comes from miscommunication or complete lack thereof. So when characters are forced to communicate the resolution is usually in the sane spectrum. Case in point Kaoru rejecting Uta clearly and Uta accepting it (as opposed to what you would generally expect from this type of story).
It is likely that Reiichi cheated, because it is implied he only broke up with his ex because Kaoru needed him. It is hard to ignore your previous love if it never actually ended.
It is likely that Uta will have a change of heart and try to support Kaoru again. She has been strongly focused on becoming independant, but in the end this is not about her independance, but the mental health of the one she loves. Her conflict with her mom is unavoidable too. In the end I guess it will be a situation where they support each other for healing.
It is likely that even if Kaoru confronts Reiichi he will not try to divorce her or leave her. Whether Kaoru will be able to still cope is a different matter. Pretty much the only way they could break up is by Kaoru's own decision.
Oh and Kuroe will grow to love Miyabi and eventually understand it too. That's probably the only outcome I can predict lol