I think their behavior makes a little more sense if you consider who they are. Heesuh is a top tier chaebol who thinks a Mercedes is a shabby hooptie. Jinmoo is also from an extremely wealthy family but he’s not at that very top percentile so he’s perceived to be a “dog.” Heesuh was raised to believe that relationships and marriage are solely transactional, theyre for business/class advancement.
Reading this comic, I’ve never thought that Heesuh actually hates Jinmoo. He’s fighting against the fact that Jinmoo is this person who causes him to have all these FEELINGS. Feelings in his world are uncomfortable and annoying. If you have feelings you might have to learn to be true to yourself. If you have feelings you might have to deal with the fact that you’ve liked Jinmoo since high school—instead of being the perfect chaebol with a trophy wife. It’s a fight Heesuh is having with himself, not Jinmoo.
Because Jinmoo is a lot more perceptive, he understands why Heesuh is struggling so much. It’s kinda like “ahhhhhh you’re trying” when Heesuh gets all pouty and whiny. I get why Jinmoo finds it so cute and adorable!