
People always love the spin-off story of the broken heart character from the main couple, but Toguto/Slen story was so weird and not convincing enough for me, sorry.

I think they just needed more time to develop. Toguto is ridiculously slow, so it took a long time for Alta’s words to actually cook properly in his emotionally repressed peabrain. Slen felt emotionally betrayed, so he betrayed Toguto to get back at him and regain a sense of control, but he never stopped feeling affection for him. The toxic environment and Toguto’s emotional density/laziness prevented either of them from moving on. It makes sense structurally, but it should have been a slower process
A bittersweet first love with someone older. It’s their culture (if you’ve been around j-movie and pop songs, you’d have known). I don’t want to say what is right or wrong. If it happened in real life in my culture it would be inappropriate.
In my opinion, if the story wrote it as an adult taking advantage to an innocent minor who still have no ability to understand what’s right or wrong, especially manipulate them in sexual way. That would be unacceptable. I would feel disgusting and will not be reading it. But this kind of coming-of-age story of Miyai is always have the borderline feelings in it. So just read it as fiction, or if it too disturbing, just skip the part.