
his mother is dying. Mia isn't just dangling the new medication over his head, she's funding his mothers' treatment entirely. we only see her refuse the new treatment because she realizes something is awry, but he is still dependent on Mia financially and this is her bargaining chip
this is not ego; he is not thinking of himself in this. it's inconsiderate at worst but it is clearly just a child's desperation for their parent to live, as well as a poor mans plight against his circumstances
and how do you even expect that conversation to go? he clearly feels backed into a corner and is being taken advantage of both sexually and financially. she pissed in his mouth to scare Jung-Woo away bro, she calls him Myung-Ha's 'little boyfriend' and gives Myung-Ha an ultimatum, demanding they break up or else she'll stop paying for his mothers chemo. he's a possession to her. no shit he didn't try to 'talk things through'

Yeah no I was referring to your second comment, yeah Myung Ha is way too stubborn for his own good but that doesn't make him selfish. He thinks that he has to do this on his own because that's how it's always been for him ever since his mother fell sick, he doesn't want to burden anyone with this be it his mother or his ex boyfriend. And yes it might be stupid but calling him selfish is wild.
Also he knows the little Bro is just as broke as he is and he knew that if he told him about what he was doing, he would've tried to talk him out of it or done something reckless to help him, which is exactly what the little bro's doing btw so he wasn't entirely wrong, plus he was probably too ashamed and didn't want the man he loved to see him like that.
and thought "omg i'm so dumb at least my boyfriend is not selling his soul to an evil woman gotta support him and be grateful"