
Can someone explain me what happened in Ch 42? Like o don't get what dohyun said and why sungho went to the other room and screamed

Many of us got confused on that too but the consensus is that Sungho got a sudden awakening from his delusional state when he saw Dohyun crying.
He has been working in a delusional idea that Dohyun needed to remember their past and that they were lovers and that's why he was redoing all the things they did .... in his twisted mind, once Dohyun remembered he once 'loved' him it will be okay and 'come back' to him.
Obviously the kidnap and raping wasn't the best way to win Dohyun back. Sungho is convinced that once remembered his advances will be welcomed but he is suddenly confronted with the reality of those tears. Whatever rage, hate and despair he saw in those tears brought Sungho to a moment of sanity and forced him to see the horror that he did. Like a crazy person who is suddenly regains sense in the middle of killing someone. That's why he retrieves from the image of Dohyun and gets his own breakdown outside ... if he got sane enough to intend to free Dohyun we don't know because all that he can say now is that he is sorry and he didn't intended that outcome. We have to see that Sungho is not a sane person so even if for us his logic and thinking doesn't make sense, that is the plot in the story -- he is behaving like a crazy person and therefore his motives and techniques is something that makes sense for him. If he walks back to redemption or sanity and do something to atone for the harm, we will never know if the story ends here.

Did he just name a slime "water"? (≧∀≦)

Ok I did some research too. I read the raws and the MC actually uses the katakana スイ(Sui), so no kanji at all. Actually the kanji you wrote (酸い su+i, it's an adjective) is the one for acid, but in matters of taste, so acid or sour taste. It would also sound really strange to give it an adjective as a name probably.
Because of this, I actually think that my random guess was actually right, I'm so happy ε=ε=(ノ≧∇≦)ノ
Anyway, you actually made me curious about Suicune and i also looked that up. Sadly I couldn't really find anything. The part of Sui is probably the one that means water (it's a water type god, so it would make sense) but for Kun, I have no idea. Maybe it sounded interesting, I don't know ╮( ̄▽ ̄)╭

Cool. It's always fun to research other countries languages. But everything non-Roman languages is hard to decipher for me especially when it can have readings then 1 and more different types it been used haha. (Which make studying Japanese by myself harder.)
If we don't know what form has been used originally then it could go both ways ٩(๑❛ᴗ❛๑)۶
But it's always fun and interesting to know. (=・ω・=)
Sui already cute even w/o that name.
BTW is Sui a girl or a boy. Someone told me before that in the novel Sui is a girl, but here it's always said "he" ( ̄∇ ̄") So confusing if Japanese speaks genderless

Like you said, it's genderless. I mean, a slime is not a thing that has gender, so the name also doesn't have one.
Regarding the name you said, you should try and look up the kanji. Even though they could have the same sound it doesn't mean that it's the same one. When it comes to Japanese names, they don't have a specific gender in it, like the western ones, they are just used more by some people for different genders. They just look at the meaning usually

Unfortunately so true. But I don't have the money to study for it. Nor really the time to really go for it. So for now only basics. Although can understand some of Anime w/o sub or listening to Japanese audio/cd drama I can sort of know what's going on.
( ̄∇ ̄") But I don't think they gonna use those words IRL, after all must watch out not to speak rudely when speaking to a native Japanese!
@.@ so many things to think and watch out for. G'luck in your studies!
I wish my dad was still alive then he could have teach me, (I'm actually halve Japanese on my fathers side), but he passed away when I was little. I grew up in the West when my mum married with a Westerner. (I can't even speak my mom's language)

To all the ones who blame the older brother for not stopping his relationships with his ex boyfriends: I hope you are not studying law or that you don't don't work in that field. Law most of the time doesn't equal being right, that's why it's people being judges and jury and not just somebody who follows what's written...
You actually BLAME the older brother because he didn't stop a illegal rape (underage) instead of seeing that the problems is the little brother being a bitch and INTENTIONALLY having sex with them?? If there is someone to balmer it's should actually be the ex boyfriends for being bastards and the parents for having grown up a little brother with such a twisted personality.
....

Well clearly you're not studying or exerting law yourself because it IS about following written rules WITHOUT being subjective or being biased because of your morals/opinion...
(also, jurys are the ones who let proven murderes/rapists go free and innocent men go to prison, or even the death row, because of bias, just watch Twelve Angry men, you'll see)
No matter how bitchy and deeply malevolent the brother is he is a kid and according to the law children are not responsible of their actions (lack of experience, maturity and/or mental capacity to fully distinguish what is right and what is wrong). And the law is, in essence, ment to protect the weak (e.g., kids). So yeah, it is wrong to let the brother get raped...
Nobody "deserves" to be raped. That's not justice. Everyone is to blame in this situation (except maybe the parents, we don't know if their youngest son isn't simply naturally deranged)
But this is yaoi land where pre-teens /very young teens act and are treated like adults because shotacon is a thing... So I guess law doesn't apply ╮( ̄▽ ̄)╭

The real question is: was Kyon doing it unconsciously or is somebody in the house doing it (like Cecilia's servant or Christoph)?

https://imggra.com/tag/chungnyun
here is the answer (๑•ㅂ•)و✧
I'm so triggered but I really don't know anymore who of the characters is to duspect. At first I thought it was Kyon, then Chiris, then Cecilia, then Ryan, then the plant in the corridor...
Author you driving me crazy!!! Good job! ε=ε=(ノ≧∇≦)ノ
the plant in the corridor that kills me
Ikr
yeah