I was wondering where the feeling of disconnect was coming from. This explains it. Cause we know taeseo is capable of caring. I mean, he sent yeomin, a stranger, to the hospital and protected him from loan sharks. So he's not entirely heartless. I guess he just hasn't fully understood yet how difficult poverty is before. He kept asking "why is this guy everywhere? How many jobs does he have" bc he doesn't know that some people really do be doing everything just to survive. Then when he saw how hard yeomin's life was, he kept wondering how the lil guy could remain optimistic. Of course, there's still a part of him that doesn't care (not listening to yeomin's babble, missing important info about yeomin's schedule, etc.) but that part is him being wilfully indifferent and not ignorance
The fact that his exes were celebrities meant that even if they were poor or struggling, they wouldn't show it for the sake of appearances. When they were with taeseo they'd probably put on makeup, wear their best clothes, and always look presentable. Unlike yeomin who carries a cracked phone, lives in a shabby rooftop apartment, and walks with scrapes and bruises. He's so frank and open about his difficulties but he never showed that he's helpless to taeseo. If I was taeseo I'd be fascinated by him too
"If I was taeseo I'd be fascinated by him too" I think that's exactly what happened. He keeps coming back to Yeomin although, according to his secretary, he never ever cared at all about any of his ex. Taeseo himself was wondering why he went back to Yeomin's place when he wouldn't answer the phone. He is definitely intrigued and attached although he's still so clueless he doesn't realize it yet!
Hold up! Could it be that all of Mr. Yeon's past partners were rich (or at least well off)? Is that why he's so baffled by yeomin's poverty? If so, it kinda explains why he didn't offer to be Yeomin's sugar daddy on the first day. I'm guessing he hasn't interacted much outside of his class (he's not the friendly-approachable type after all)