Brown hair does know? She literally told him in the opening chapter? She’s not gonna suddenly become bi after coming out as a lesbian, that’s generally not how sexuality works. And why would ML choose now of all times to suddenly start interfering with MC’s crushes? They may be exes, like MC suspects, but at the very least Hyuna seems to be aware that ML has an unrequited love for MC that he’s never acted on because he thinks MC is straight. That’s why she’s confused and asking ML to explain what’s going on

I think the brown hair girl is not his ex,I think the black hair man rent her I mean give money to act like to be girlfriend of that black hair girl so the brown hair man don't have any chance to his crush.