Why do I feel like big sis is trying to play cupid and force her twin into action? Hm

play cupid? she looks like she’s ready to kill someone

I have to wonder if she happened to see them go into the love hotel that night, and got pissed at her brother for not telling her that he was gay, and decided to pursue her boyfriend as a means of getting revenge on her brother for lying to her. Not necessarily realizing that they might have feelings for each other, but just to needle her bro into feeling guilty because her new "boyfriend" is the same guy he had a one-night stand with.