I read up a bit but not much for now. everything after is spoiler.
The blonde man in the practice room is another student of the professor, but like yerim who's taking psych meds for her anxiety, he's also a recovering alcohol addict and has almost completely quit playing piano because he's lost his "sound". They become friends and Krueger (the blonde guy) brings him to watch one of his lessons with a new professor, where Garam realises that the professor's lessons are much more violent and harsh and other instructors can teach other things.
He tries leaving the professor's house because he realises he can't hate him anymore and his feelings might ruin his "sound", but the professor is so desperate to keep him from leaving that he kisses him. After that they kiss a couple more times but the professor is in denial and keeps saying he doesn't like Garam, and Garam also feels shitty about the situation. All this is made worse by the fact that Claren is a super fan of the professor (they've slept together before as well) and he keeps treating her very nice and not rejecting her advances.
This is a vague outline until chapter 95, there's other things going on in the background as well, the artist is a genius.
major spoilers
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theres gonna be a lot of push and pull, especially from the professor’s side. you’ll probably hate him for a while theres even a scene before they properly get together where he has a one night stand with a woman (im assuming it’s the sponsor). Ionly read the raws and I don’t speak korean, so take this with a grain of salt, but I think the professor has some trauma around being abandoned, so he keeps trying to push garam away. garams persistent though, and he doesn’t give up. They eventually kinda get together after their concert, where they perform a duet. garam surprises the professor by playing one of the professor’s original compositions. all of that happens around chapter 120. after that, they have a lot of sex throughout the following chapters, but it’s still very plot heavy. also, there’s this part where garam plays a duet with the professor’s ex-student (the blonde bearded guy), and the professor gets all jealous hehe.
the sex scenes in this manhwa are some of the best I’ve read.everything feels so raw and intimate,but the professor is hella rough but garam likes it

Someone plss spoile little bitttt(⊙…⊙ ) iam so eager to know what will happen next( ̄∇ ̄") ヽ(`Д´)ノ