Yeah I dont think its out of jealousy. I think he must be feeling really lonely, looking for someone who can really understand him. Maybe because he had ambiguous feelings for Heejae when he was one of his students. And I also think he really wants to help Garam in his own way. But he doesn't understand their relationship and this is putting Garam on the spot
it's definitely hatred.
if you recal from the earlier arcs of the story, heejae's teaching method completely revolved around getting his students to hate him, in part so they wouldn't try to copy his music style but instead develop their own "sound" (his process for turning them into "gems"), and in exchange he opened doors for them in the classical music world and propelled their careers to greater heights. we've gotten to meet three of his past students and seen how that hatred and their experiences learning under the professor have shaped them into who they are today. for compton, that hatred for the professor is very much still fuelling him and he is on a mission to "free" garam from the professor's influence, like he apparently freed kruger and choi, probably in part to punish heejae and make him suffer.
in all honesty, compton's reaction is completely fair. remember how much we all hated heejae's teaching methods? it's not surprising that compton could get to the point of hating heejae so much that he would begin actively sabotaging him whenever and whereever he could. obviously, it's not a healthy response- but it wasn't a healthy experience either. i think ultimately, compton is still suffering. he isn't as "freed" from heejae as he thinks he is, since his hatred of jae is still influencing him sooo much.
I saw someone else say something similar to this -
But it seems like Compton’s reasoning to pushing Garam away from Heejae might be out of hatred, not jealousy. I think that if it was jealousy, Compton wouldn’t be so patient with Garam. I’m excited to see where this goes and yes Heejae, crash out for your boo we know you love him to death hahaha