"letting his sister to beat her for so long and then wanted to fuck her" you just described almost half of the male leads in those manhwas. The amount of male leads that torment the fl or letting someone else torment her is unreal, but all you need for a happy ending is a reincarnation (in which the fl suddenly realizes that the ml loves her and turns a blind eye to her past suffering), an escape plan (in which the fl runs away, the ml realizes how important she is to him and starts to look for her all over the country, and when he finds her she accepts him) or death. I personally prefer the death route in some of those manhwas
The male lead sucks but he's not the worst male lead I have seen. He may be trash, but at least he's recyclable trash. The male lead in 'if you wish for my despair' for example is a non-recycable trash that can't even be called a human. Even calling him a beast or a bastard would be an insult to beasts and bastards