Jihan always pushing the sunbae away and rejecting a more serious relationship was already valid, but with this extra context it makes even more sense. Despite his first relationship in high school, Jihan started to trust and fall in love with the sunbae. But then he caught the sunbae with some girl. The same exact scenario as the high school bf.
Even if it was because of the mom, even if it was a misunderstanding, that doesn’t matter. His trust was completely shattered, and all of Jihans fears and anxieties surrounding love were confirmed.
if the sunbae sent ONE text to jihan about having to cancel their plans last minute, this situation could have been avoided. He could have properly explained the situation (assuming it actually was a set up date by the mom). Jihan probably would have started dating him.
But he didnt. He’s lucky jihan still has sex with him. He needs to accept that jihan will never trust him again and move on