HUGE SPOILERS AHEAD
So that figure is actually for someone that used to work as heejae's manager that looks EXACTLY like garam, acts like garam, says and does stuff that garam does and he was the only one who liked heejae even tho knowing his horrible personality.
Anyways he got kicked out from his house and then started living with heejae then heejae heard him play on his piano and he had a very unique and beautiful "sound" and heejae was surprised cuz he didn't know that he could play the piano especially this good and works as a manger. So long story short that dude is dead and he's actually the reason why heejae even started this whole mission to look for the perfect gem as yerim "it's as if he's searching for someone/something". I still don't know how he dead I'm just starting in season 5. But I guess they both had a huge fight and he left just like everyone and got into and accident? Idk also I think that garam might be that same dude reborn? I mean heejae said it himself "you finally came back to me so I won't ever let go of you again" . Also I don't think heejae and that dude ever got to date but they definitely both loved each other A LOT
No he doesn't date garam cuz he looks like his old lover, he does truly love garam. But he can't help but find similarities between them in terms of actions he never compared their looks or anything but they do look a lot alike. Heejae deeply blames himself for his manager's death and doesn't want to make the same mistakes again with garam
Nah dw the story is still peak. Heejae absolutely DESPISES that garam says stuff that remind him of his manager and he hates that he keeps seeing his figure, that he will genuinely lose it and go berserk on everybody damn I feel like I spoiled a lot the story only gets better and can't wait till we get to chapter 101 literally my fav chapter so far

Whose shadow did he see leave? Kruger? Or the last student we haven't seen?
Also, he didn't hug back... I'm so nervous for Garam now...