From the Illness****************

The Female Protagonist Is Sickly, the Male Protagonist Is as Gentle as Jade and Well-Educated, but the Female Protagonist Pulls Her Down from the Altar.

I want to read a book similar to "The Yandere Princess is about to turn black, and her brother is holding her and coaxing her". The female protagonist is really crazy and the male protagonist is very gentle or abides by etiquette. In the end, he is led astray by the female protagonist or redeems each other.