The approval plot rests on the idea that one of the lovers is not acceptable in some way due to--oh, name an issue. However, the other lover stays true...
And, honestly, it isn't a completely horrible storyline since loyalty is very attractive.
The problem with the approval plot is that ultimately there is nothing else there. The Thai drama, Secret Crush on You, is a case in point. Three "misfits" date three handsome, popular young men. Rivals show up, amazed that the popular young men don't know better. The college campus expresses its dissatisfaction through social media (it doesn't seem to occur to any of the characters to simply throw their phones away--yes, one can survive without a phone!). In the meantime, the misfits sit around and console each other. Every now and again, they adopt a stiff, upper lip. Or they deliver sermons to each other and the camera about the horribleness of the world and the need to believe in oneself.
It's rather like watching a fictional version of a self-help cult. And from a writing perspective, since the characters' stiff upper lips rarely translate into anything that resembles a distinct life choice, there's nothing there.
Pride & Prejudice concludes with rich, handsome Darcy demonstrating loyalty to Elizabeth and repairing his mistakes through a series of deliberate actions. In the meantime, Elizabeth takes responsibility for her misreading of Darcy. She also stands up for herself with Darcy's aunt even though she believes that the relationship with Darcy has ended.
The final point is an important one. Lydia's behavior could have sabotaged her sisters' chances at good marriages. Yes, it is marvelous that Bingley and Darcy rise above it all--but Lydia's behavior was truly thoughtless and damaging, having actual impact on real life outcomes. Judging the family by Lydia's actions isn't--for the time period--a "bad" or "toxic" (a useless meaningless label--will writers stop using it?!) mindset that "shouldn't" impact "correct-thinking" people. It's a real plot problem from which Elizabeth isn't rescued (the reasoning behind a rescue seems to be that the scandal is sooo unfair, the fallout "shouldn't" be happening). Rather, she manages the problem and maintains her integrity.
Cherry Magic! The Movie demonstrates an Austen-like focus on self-responsibility while taking the real world into account. In the movie, when Adachi is hurt on the job several hundred miles away, both he and Kurosawa are upset that the nature of their relationship means that neither work nor family members contacted Kurosawa. So they determine to tell both families about their relationship. No blame is parceled out regarding anybody's close-mindedness. No lectures are delivered. No labels are applied. No assumptions about "well, you are cisgendered and heterosexual so you won't understand how much harder it is for us" are utilized.
Instead of "here is how people ought to behave," the two men start from the realistic position of "here and now is what it is--and what we desire might take time." They also treat each family as a group of individuals with their individual perspectives and needs and issues. Everybody has a personal life--here is ours. We hope you can meet us half-way. They brave the unknown and take concrete action rather than waiting around for what they are supposedly owed by society or the universe or...I have no idea. Each man accompanies the other to his family's home. Each man speaks his intent and his future commitment while demonstrating respect for his lover's family.
The result is more romantic than all the self-help speeches in the world. And healthier.
Likewise, Dew in 609 Bedtime Story doesn't blame his parents or fiancée or society at the end; the terrible events in the alternate universe lie, ultimately, at his door. He takes responsibility.
For a character worth investing in, what-is proves more fascinating in the long-run than what-ought-to-be.
