It wasn't that Jaekyung's sleep got interrupted by Dan's coming in and out of the place with the door shutting, Joo was already awake in that flashback. He would have frowned and squinted his eyes upon opening them if he woke up from the noise.
He was annoyed that Dan left that luxurious place, his place, to go somewhere else. Likely meet someone else in his mind. When he asked ''what sort of gig?" He immediately thought he went to sleep with others and was surprised that a ''pretty but desperately dirt poor'' man like him doesn't go the ''easier'' route but taken an honest job.
What were all of you expecting lol, it'd really be satisfying to see Jaekyung being grateful, happy an praising Dan? xD ofc not, that'd be out of his character, and he was so pissed bc he was actually worried and more pissed bc he couldn't sleep well with Dan going in a out the house at night xD, I agree, the man is broke and has one job, two in fact, just focus on that please stupid Kim Dan. People, read the room, I really appreciate de consistency and coherence Minhwa maintain, just my opinion ofc.