spoilers below!
if zec follows the novel, this should be resolved in the next 1-2 chapters! bc in ch 18, there was the whole issue of the pension not being booked for the workshop. so after jongchan fixes the issue and the team actually goes to the pension for the workshop, they have a dinner party at the end. and team leader choi scolds seunghyun in public and thats when jongchan realizes just how much he adores seunghyun and how angry he feels when he can't do anything to protect seunghyun.
so jongchan decides to talk it out with him again and they have this super hot/intense elevator kiss ヾ(☆▽☆) after that, they have an actual conversation where they both realize that they need to see things from each other's perspective. from that point on, they decide to properly communicate and to not keep any secrets from each other. and they get back together (⌒▽⌒)
I have read the novel! Spoilers below
The first sex scene in the webtoon is ch13-15 but that is only intercrural sex. The Korean webtoon raws are up to ch 18 right now and based on how long the webtoon chapters are and if zec continues to follow the novel, I’m guessing we should get a penetrative sex scene around ch.22-23?? (▰˘◡˘▰)
i did read it in korean & i used to be the english fan translator for this webtoon actually ╮( ̄▽ ̄)╭. i'm cleaning up my translations for ch 10-13 right now so i can post them here. and i think i'll write up a post about novel spoilers to include too... but to answer your questions! (below cut)
in the novel, i dont remember if the ex's feelings about their relationship are shown? but based on how he tried to set up jongchan and seunghyun in the first place, i think he would have definitely approved!
the chief and his ex had a really casual relationship which was almost like friends with benefits because they both are workaholics (this is mentioned in ch 12? i think).
seunghyun and chief start dating after the kiss in ch 9 although they're not in a full relationship just yet. they have sex for the first time from ch13-15. and then in ch 16-19 (probably up to ch 20 or 21) the relationship drama starts because seunghyun finds out that chief's ex is his first love.
jongchan/seunghyun get into a fight about this and break up (and tbh i understand both of them here, i think both had valid reasons). this is the frustrating thing that OP was talking about! thankfully in the novel, they get back together pretty soon after this and after that is when they have a lot of cute & hot sex.
hope this helped!ヾ(☆▽☆)
The last few days i've been reading manwhas and mangas where if there's a trouble is solved quickly or rather the history is advancing rapidly and this only feed my angst (I'm in chapter 18 in spanish). Mr. Pat do something and Seunghyun you asshole stop being such a drama please