This wouldn't happen if it weren't for the uke CUZ wHY did he accept the proposal and marry her FOR WHATEVER REASON. However as I see it, he's still inlove with the seme the sister wouldn't be delulu if he didn't involve himself around her and the seme wouldn't have a fight with her sister
I think Uke accepted the proposal as a sort of revenge on the seme since it seems like when they were dating the uke would get angry that the seme prioritized his sister more. Plus, the sister was really freaking adamant about marrying the uke. I think the uke was always in love with seme and probably hates the sister. But I don’t know, the Uke is still an asshole for marrying her and the sister is an asshole for being so delusional to the point of being dumb.
Zhen hao and his little bro sure are polar opposites