Ngl, I thought that too but then I sat on it and realized that that would be a bit redundant cause wasn't that kinda how this arc started? While it wasn't necessarily a breakup, Garam went to europe to find independence from Heejae, but that was totally hijacked by Compton playing in his face to get a one up on Heejae.
It's possible that they'll have a huge fight, but hopefully they will talk their feelings out especially Garaam. I don't want them to break up, but it's understandable if they did.
Spoilers
In the recent chapters, Heejae took revenge on Compton for criticizing Garaam sound and he took that to heart. He decided to make a scandal on how Compton treated his previous students and he was cruel, etc. Garaam of course didnt mind the criticis, but Heejae didnt care and ends up leaving Heejae while they were eating at a hotel. After, Heejae goes back to their hotel room where he finds Garaam crying. Garaam wants him to apologize and explain that he didnt have to do and he didnt want him to do that. Of course Heejae says, " why would I apologize, im doing this for your sake." And then it shows Heejae stabbing Garaam ( visually, not physically. Garaam then wonders if Heejae cares more about music rather than him.

What if season 5 ends with them breaking up