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He doesn't. I wont say everything since the away from new York arc is extended till ch 186. But heejae figures out his own feelings after garam gone, he realises he doesn't want to be alone, and that he could purely enjoy music if garam was by his side and well, the presence of his ugly emotions closes up and disappears. He find out that he genuinely loves garam despite being a knife, and that he misses garam a lot .after that he gave garam a surprise visit in London even though his Bo, Pv, NY (Boston, Pennsylvania, newyork and Cleveland) tour starts in a week. Both of plan to keep their relationship hidden after all the bullshit compton put garam through. So there's a lot of secret meet ups and jealousy scenes. Garam figures out finally how to play rachmaninov, as he embraces that piece as heejae. So after ch 162, it's all romantic.
Can't really say this definitively since I'm basing off the author's ig posts and not the raws, but nothing like that happens, they actually make-up pretty quickly. Besides, I don't think Heejae would actively seek out Claren now that he and Garam are a thing. Not sure how "official" they are but they certainly have something more going on between them as compared to when Garam was pre-debut. But yeah, whatever he and Claren had at the beginning is most likely to stay in the past. If anything, Compton's probably more of a threat to their relationship at present since he's actively (and very openly so) trying to save Garam from the knife that is Heejae.

please please please give me spoilers if professor seeks out claren again while garam is away at england or if he doesn’t even go, pls js spoil the whole england arc for me pls