Did you? His ex injured him during the sex (probably because of inexperience, probably because he was not in the right place mentally because he had a huge bruise on his face). He saw the blood and puked. Mc connected the dots by thinking that the ex was disgusted. If they had spoken, communicated sincerely, things would have turned out differently.
By the way, mc still suffers from this thing during sex with other people. That's why they shouldn't have dragged the matter and at least talked about it. Maybe they would have broke up anyway or maybe they wouldn't. In any case, mc still thinks about him. And the sunbae is totally still in love with Mc. In all of this, I only feel sorry for the girl.
Then the dynamic between ml and mc is fun, don't get me wrong. But I would have preferred to see something else. Reality check on ml. He is an immature kid, obtuse, all too sensitive, and above all obsessive. Although I don't think he did certain things with malicious intentions, he still lied about his brother's death for personal gain, and it's clear that the dynamics of when he was a child are repeated with the people he relates to

Man the misunderstanding between mc and his ex is crazy. They could have literally just talk it out and solve their problem. They would probably still be together rn