He is not just enduring this for money tho he is already in love and cares so much about him despite the fact that not even being treated like a human being. I think that is why commenters are annoyed
There is that too. His entire life he felt like he was a burden to his grandmother. Who must have gone through a lot of hard time raising him on her own. So in return he doesn't want to become a burden and want to help out as much as he can.He was able to help him out in his time of need with the thugs, financially. The fact that he even went to the hospital and have a decent conversation with his grandmother. So yes you're right he is having some feelings. Ignoring all of the red flags and abuse.
We have to remember that he was raised by his grandmother. He was raised to be polite, helpful, respectful and appreciative. He must have been treated awful almost He's entire life. He will do whatever it is he needs to help his grandmother, and not wanting to embarrass her or bring her any stress. So despite the bad treatment he's receiving from jaekyung,He still was able to help him financially So he's going to continue to ENDURE this bad treatment. Until the plot twist.