Spoilers....
I may have gotten the wrong impression from using machine translations when I read the raws, but at the end of this arc, Compton wonders if all along he had actually held affection towards Heejae. Rather than a romantic interest, Garam was a mirror of who he would've been if Heejae recognized his sound instead of rejecting him (as his protege). His need to frame Garam's feelings as hatred, and his insistence to deny Garam's love for the professor, almost felt like a like desperate attempt at self-correction. He was actually projecting himself on Garam.
I feel like he may have had ambiguous feelings that he himself did not realize. I don't think they were strong enough to be called love, but they were rooted in a deep desire to be recognized and acknowledged by Heejae. As much as he's driven by his hatred of Heejae, he's also driven by that longing. And that's reflected in his last conversation with Heejae where he asks what he thought of his music now. Well, you can guess how heejae responded.
Hmmm I think this makes much more sense. Thinking about it now I don’t think Compton necessarily had romantic interests towards heejae. Rather, he seems to look at garam in a “that could’ve been me”, way (like you said in terms of being a protege). Now it seems as though Compton simply hates heejae, but I think we will come to find out that he also just wanted his approval more than anything.
I think when compton sees the way heejae treats garam, and he will blame himself and therefore project that as hatred towards prof. But I’m sure part of him simply hates heejae since that guy is an ass of a teacher!

Did compton have feelings for heejae or is that far fetched? The flashback heejae had of Compton crying in the ran looked a lot like the time garam was crying from being “rejected” by heejae. Also Compton seems to be really perceptive of other’s romantic attraction. Like he quickly caught onto Walter’s feelings towards garam, garam’s feelings towards heejae, and the other musicians’ romantic affairs. I could be wrong though.