But tbf dan didn't ask for him to pay his debt and stuff which mean Jaekyung did allat on his own accord and Dan feel like he is obliged to repay him back. Also even if he doesn't hold any feeling toward Jaekyung, he would definitely still went out of his way to get Jaekyung an expensive gift regardless
Furthermore the choice of the gift for Jaekyung was actually very smart? Like it's not something over-to-the-top at all or make the receiver feel awkward about receiving it. I think the reason why Jaekying make a big deal out of it was because he thought those trouble Dan went through would impact or make the treatment less effective and that will affect his jinx or something ig
He can be mad but there is a difference between being mad and getting downright nasty. He chose to pay for Kim Dan's debt because he also needed something from him. It was a transaction, a business. If so, he should have treat him with respect as a human being. For sure he can find someone else to do Kim Dan's job, but he won't find someone who truly cares for him like Doc Dan does.
tbh jaekyung has right to be mad bro paid for his everything and got him living in a penthouse just to make sure dan is doing his job well just saying happy birthday and cooking a nice meal would be better than tiring yourself enough for a random Keychain