He takes away her agency, not allowing her to live her life the way she wants to (as of episode 24). There are a lot of lousy men to the FL in this drama but I think that the fact that he is her brother makes his treatment of her worse.
I'm really starting to hate this series. The FL is smart but she can't make the best decisions because the ML and his friend keep wiping her memory and making her forget the bad things that happen to her at the hands of others, leaving her at their mercy... If he's not going to tell her the truth, he should protect her a lot better, but he's doing a piss-poor job so far... I'm on episode 29, there's still no sign of the ML finally being honest with the FL and of them getting together. The only reason I'm not dropping this is that I've come too far already...
I can forgive a lot of stupid and misguided things that some drama characters do in order to "protect" loved ones but I can't forgive the male lead in this case. By erasing her memory of "that night", he's not protecting her, he's just leaving her at the mercy of her would-be-rapist.
The first 5 episodes are out.