
There are many possibilities!! Either he does something to the sunbae or he force himself on the uke & punishes him senseless yk how... Or he stays calm & manipulate the situation to his favor or he guilt trip the uke & expose their relationship.
I kinda feel sorry for the Sunbae. We all know these two toxic brothers gonna prevail but why bring someone innocent to it? Sunbae! The man you love & is in a relationship got filled up to the brim while you're just exchanging saliva. Top probably feels like he's being cheated on.
A part of me is excited & A part of me is disgusted. A Part of me wants to see Seme going crazy in jealousy. Lmfao. While a part of me wants to see uke railed. Heck yeah! ┗( T﹏T )┛

Ilay & Tay should have been reincarnated into an omegaverse genre given how Ilay goes feral wanting to mark, cum, literally impregnate Tay if he could. Just look at that man, He's never SATISFIED. Lmfao & even after all that he says he's not sure if he likes or loves him. And he MOCKS Tay when Tay ask Ilay if he likes him. (if i remember the novel correctly)
Maybe Ilay keeps being in denial too because his feelings are not pure & naive enough to be called love. He doesnt know what love is or the right way to like or love someone. His way of loving Tay is unhealthy, toxic, obsessive, like the kind where he'd literally chain him up or is the type where he is HELL BENT PASSIONATE on making him his irrespective of whether Tay accepts it or nah. (Some might say that's not love, but i use the word love loosely because Ilay's brain don't function like a normal person but that of a psychopath. Given how he came to the conclusion that he has to know that Tay is his for him to feel assured & Tay's body has to know it too.) Make it make sense. ╮( ̄▽ ̄)╭
It can't even be called love in an innocent, pure or traditional sense so Ilay probably gets confused & all he can say is, 'YOU'RE MINE.' because he probably can't comprehend what loving or liking someone is or justify that just because he wants Tay & Tay drives him crazy, it doesn't make it like or love in his book. If that makes sense? (〜 ̄△ ̄)〜

Kinda realistic how they're arguing for nothing. They're arguing because they're not communicating. Lmfao. LDR sometimes does that. ┑( ̄Д  ̄)┍
The seme expects the uke to tell him every single detail while not applying the same rule for himself. He becomes condescending in text messages & calls, is needy, clingy, wants the uke to bend backwards for him, expects so much attention from uke while he does the total opposite. Bruh!? Come to your senses before JUMPING to CONCLUSIONS, getting mad at someone for returning the same energy you were giving. Σ(っ°Д °;)っ
Like fr!? He's like a TEENAGER who's going through puberty who can't control his emotions. (╬ ̄皿 ̄)凸
All I can understand from this is that... The father wanted to be portrayed as a loving father to her daughter infront of the society & people, probably increasing her marriage prospect & value in the process as well. He maintained a facade of a man who cherishes his daughter infront of the world just so he can get the best deal out of her marriage Given the time, I bet it was for his own IMAGE & benefit, it was never for the FL ヽ(`Д´)ノ
Even though FL knows it herself that her purpose in life was to marry into a family that her father chose yet she had not accepted any incoming proposals & kept rejecting them because of her own worries & illness. That probably drove her father mad thinking she would refuse to be WED & he did what he did in a round about way. AT FIRST HE DIDN'T HAVE TO GET HIS HANDS DIRTY BECAUSE THE STEP MOM WAS PLOTTING AGAINST THE FL BUT WHEN HER PLANS GOT REJECTED, HE STEPPED IN.