i think you might be misunderstanding the quote you've cherry-picked. jisung isn't saying that leaving him the way minho left was the right thing, but instead that taking the job was, which is something that has been articulated a lot in this fic, because minsung are both career-driven and they understand that desire for more. the whole thing could've been solutioned with them flying back and forth between seoul and tokyo without even a mention of divorce, and we wouldn't be having this conversation at all, but then the fic wouldn't exist. it needs drama.
jisung's hurt and resentment is a constant topic in this fic. he feels guilty, because he loves minho despite what he's done. and him talking to minho and agreeing to get close again is crucial for them to even begin working out the issue of minho leaving and all its consequences. how could they both realize the actual weight of it if they stayed far away? and just because they get together, it doesn't mean everything is alright again. the anxiety follows jisung all throughout the fic, and it doesn't leave just because minho says he's sorry.
if jisung had no self-respect as you say, he wouldn't be anxious, and scared, and he wouldn't keep pushing minho away every time they did manage to get closer. instead, he would've jumped into his arms from the get-go and they wouldn't even have one conversation about it. he's sort of an unreliable narrator. i thought that the scene where he has heart palpitations would be enough of an arrow pointing at the fact that he's a) in denial, b) having contradictory and inconsistent feelings about the whole situation.
as for jisung's friends, yes, i do think them meddling because they know how much minsung love each other and they know that they just need to talk is normal. the point is that they weren't taking sides, because they were all friends, and all they wanted was for minsung to be happy together. jisung was annoyed by them, sure, but he's a grown man and if he really hated it, he would've told them to fuck off and yelled at them the way he yelled at minho in the locker room.
his mother is a different thing. she's overbearing and she doesn't know the limits, and i haven't said anywhere that it's right, or that jisung's relationship with her isn't complicated, because i thought it was obvious that there's something wrong there, but since we're seeing it through jisung's pov and he loves her despite it all, he doesn't explicitly say, oh no, this woman is incredibly toxic.
still, none of these people acted with the objective of hurting him. i don't think that setting him up for lunch with minho or not telling him that he'd be tagging along for an outing and "helping with intervention" is as terrible as you paint it to be, especially that, as i said: he could've told them to fuck off. he could have walked out. minho even told him they didn't have to do this, and jisung literally said that he would give his piece of mind to seungbin after they ditched them. and sure, i could've included a written-out conversation where they apologized for it, and now i wish i did because obviously it's better to have things stated loud and clear instead of hoping that the reader can come to their own conclusions.
thank you for the helpful tip, though. next time around, in the name of telling instead of showing, i will simply spell everything out and make sure to create an objective narrator so that nothing remains unclear 💗