Hii, sorry but I disagree There will be some slight spoilers in what I'm abt to say so don't read if you don't want to.
Heejae slept with Claren as a release of his anger not because she asks him to sleep with her to be sponsored. In the previous chapters we see that the professor wants to have rough sex with Garam and wants to hurt him. Him having sex with Claren that night (she even says he was rougher than before) was both to release his anger for Garam but also because he is scared of hurting Garam during sex (that's also why he says they can't sleep together and he'll explain at a later date). Also we're never shown Claren pressuring him to sleep with her, and I don't believe she ever would because she's a lover of his playing first and foremost and she greatly respects him.
To prove that this isn't him basically prostituting himself for sponsorship, after Heejae and Garam get into a relationship, Claren catches on that they're together and never once gets upset or flirts with him, because that's not what she's after. Up to chapter 201 she keeps helping them out because her main objective is Heejae's playing and, to a lesser degree, Garam's refreshing interpretation of piano pieces.
i get what you mean, and i think both our interpretations are true to a degree!
I read up until 201 so I know she will leave the prof alone when she understands his' and Garam's relationship!
I just think she made a few too many power play comments in the past and got her will by reminding the prof that she’s the sponsor, by not believing that the relationship between Claren and the prof is supposed to show a different kind of power imbalance dynamic in relationships.
I don't think she outright pressured the prof to sleep with her, but because she has the upper hand in their relationship, there is an implied pressure to not reject her.
but i agree, the prof also had to let go of some steam.
but after they slept together, he just stares into nothingness and asks her „will it always be like that“ (or smth along the lines of) which reads to me like „do i have to continue to sleep with you and listen to your stupid opinions to keep your sponsorship“
Claren is shocked by that because she understands that for the prof it’s not the same business transaction as it was before and something changed in him. so she accepts it in the future bc she is genuinely a fan and thought their admiration was mutual.

marked as spoiler since new people are picking it up and i dont wanna spoil them
i know it‘s bad that the prof slept with Claren but he basically has to bc she sponsors him AND most importantly Garam, too!! she found him at the bar where he was getting drunk, and when the sponsor wants her part of the deal, he couldn’t say no, bc Garam‘s debut is coming up super soon. She also stressed the prof the f out about the pieces Garam had to play a few chapters before.
I know it sounds stupid but ultimately he slept with Claren for the sake of Garam.
In the art world even for a successful pianist like the prof it is not enough to be talented and hard working, you still have to do the networking and the hand kissing. I also think that’s why he was rougher with her because that night he resented her for having to sleep with her.
the prof felt obviously super guilty for sleeping with her, i mean look at his face when he comes home