Because she's encouraging Soliel's unfaithfulness, and towards her sister on top of that. You could also say, why is she acting like that even if she's in love with Soliel and Soliel returns her love, he's still already married with her older sister; that's just how life works... that being said, Soliel is also very much at fault because if he couldn't remain faithful, he should not have married Iliya in the first place. But he did so anyway, so he knowingly put all three of them in this position where he would end up hurting Iliya massively. Also, this manga is showing only Iliya's point of view, but it's enough to infer that her husband and sister has been sneaking around her back, probably with her parent's support (it'll all make sense later why this is happening). Those who have read up to the latest chapter of the novel would know there's a lot more in play than just the 3 of them, but back to the point of the little sister, it's still shitty behavior regardless of all the circumstances and external forces at play.
I guess because she's disgustingly dense. In real life, there's NO way you'd miss all thenhints that bastard is showing unless you were deliberately ignoring it or being dense. Either way, if she cared for her sister, she would notice the difference in treatment they get and get mad at thqt thankless guy. Unfortunately, lil sis over here has the emotional intelligence of a bear. Her EQ is null.
You're insulting bears lmao ╮(￣▽￣)╭
Do you have the link for the novels
https://hermitranslation.blogspot.com/p/index.html (=・ω・=) Enjoy!
Thank you
Being ambiguous with your sisters fiancé is the way life works? Cheating on your spouse with her sister is the way life works?
why are yall mad at the little sister like we get it she is getting in the way of the FL but that's just how life works