While I understand it's irritating im gonna try to explain what I think:
First i'm glad they didn't make "love" make all his grief magically dissappear. MC has lived with "living" corpses for more than a year, he hasn't had any contact with anyone else other than those corpses which were his only family left after his own family died AND those corpses were only like that because HE made them like that OH AND he did it not only because he didn't want to accept they died but also because he wanted to live, he didn't want to die (back in the second great dungeon). So yeah I understand he keeps going back to square one, that's a pretty fucked up past, he's not gonna over come it only because people were being nice to him
Second, i'm also glad the author didn't make ML magically change because of love, he's arrogant and controlling, he's someone who thinks that can control everything and everyone so yeah of course he wouldn't notice all the suicide signs MC was showing. ML has never loved anyone before so I understand he only realized he loved MC was when he realized he couldn't control MC and that MC would die (as he tried to off himself)
I explained it better in my main review here: https://www.mangago.me/home/mangatopic/21019810/
I highly suggest you actually finish the story then
im on chapter 75 and im not sure if i can finish this lol, if you're the type to start getting irritated with slow paced plots and yet only having some few chapters left i suggest you shouldn't read this at all
the mc is severely depressed, i just wished he was given the opportunity to undergo several therapy sessions in between the dungeon raids to show some semblance of improvement to his mental stability and character but the mc always goes back to square one, it also doesn't help that the ml is sort of giving mixed signals to the mc and using "sex" as a sort of replacement for therapy which the mx severely needs lol
its a shame because the premise of this is really good, i actually got hyped around the early chapters !!
tldr: mcs should get therapy why is it not normalized or why is mental health issues not addressed well in yaoi