I see this take on other platforms too, and at what point do we have to stop pretending that they weren't lovers, or at least while not in physical relationship they're in this deeply emotionally not so platonically involved, to the point where Heejae spent 10 years on a mission to cope with his death lmfaooo.
Yes, I am aware that the manager "ghost" is pretty much a representation of his guilt, regret (not entirely towards garam) and eventually fear. It's not rocket science, but please, this man threw away his maestro career to find a "raw gem" in South Korea after the manager's death, then tortured young students because they couldn't give him the dopamine he got when he discovered the raw gem that was the manager.
The manager "ghost" was there after he fucked Garam for the first time, and his monologue was something along the lines of, "Beneath my passion, my true mission is to not lose you again." Then there's the whole Horowitz thing between the manager and Heejae, chapter 137, and so much more.
At some point, we should accept the possibility that, to some degree, Garam was serving as a replacement for the manager. Heejae lost someone who could understand his soul like no one else, spent 10 years on a mission after losing him, and then found someone who lit that spark in his life again in Garam. The manager "ghost" has always been there at every step of their relationship, and I think that moment in the Compton arc, when he saw his presents in Garam's room and was flooded with memories of Garam, was a catalyst for Heejae. After 160-something chapters, we've seen him start thinking about Garam instead of being consumed by memories of his past with the manager.
I do believe he loves Garam for who he is in his own way now, but yes, Garam did serve as a replacement. Id be super shocked If the were purely platonic because then why was that damn ghost was there when heejae destroyed his student ass lmfaoooo
I'm confident that if Garam finds out about the manager and get a glimpse into their past from someone, let's say Eva or Glasses Guy, and mentions his name to Heejae, he will physically lash out, just like he used to when he felt threatened. That's how little I trust Heejae.

So glad I binge-read this now, so I didn't get lobotomized by Heejae’s caring-lover display for 30 something chapters out of 209 chapter, during Compton arc and became his lawyer defending him around because he is simply not a good person and desperately needs some real, hard lessons.
He was physically and verbally abusive at times in the first 100+ chapters, abused his students for personal motives, and pretty much projected trauma and dead lover onto his new one until around chapter 160, that's more than half of the whole manhwa. Nothing can excuse his sorry existence because even his trauma from being left behind was ultimately a consequence of his own actions. He wasn’t even raised in some harsh environment that shaped him into a human blade to protect himself, he was born into a classical musicians’ family, supported and provided for in his music career from a very young age, a family rich enough to leave their kids houses in foreign countries as part of their inheritance. That's a golden-spoon nepo baby through and through. He is too old to be acting this way, irl a 45 years old like him wouldn't get this much of graces, sympathy and reasonings, you know you would hate an emotionally constipated privileged man.
Heejae letting a boyfriend 22 years younger than him be the provider and nurturer, to be the level headed adult in their relationship is pathetic. Their relationship is so one-sided, with Heejae taking and demanding everything from Garam without even being able to give the simplest thing in return, while Garam is expected to accept all of his shortcomings, he has taken Garam for granted for a very long time. There’s a whole power imbalance there too, but that’s for another day. His chasing, learning, yearning arc better last a long and satisfying after watching his being pathetic human for 200 chapters.
That being said I do love author art style and this is actually a well written story, a fresh air in the middle of slops.