The author is a woman. I still agree with your points, though.
I know, but it didn't seem worth it to correct that person and now I kind of regret quoting them without doing so. The vast majority of yuri is actually written by women.
Either they break up, or their relationship is now a series of misunderstandings to keep it interesting. Normal, angst free relationships aren't considered interesting to readers, so the writer is trying to spice it up.
In fairness its kinda tough to keep things interesting and I don't think there's many editors that would let their mangaka continue their series without spice. The "plan" in manga is usually to drag things out as long as humanly possible and then power through the finale in one volume max. Some series switch focus to side characters, while a lot of shoujo tends to focus on insecurities, especially when someone else or theoretically better gets added to the mix. We already went through that somewhat with the 'flowerbed prince' so it seems kinda soon for that but -- if the formula works it works.
I'm not trying to speculate but my hope is that Kase comes out to more people in her orbit; people on her team know she's dating someone but no one actually knows its Yamada.