Please recommend an ancient romance novel. The female protagonist is a killer under the male protagonist, and the male protagonist begins to like the female protagonist's sister?

This younger sister of his was of noble birth. The female lead was born of a concubine and did not have much status. The male protagonist liked her sister and asked the female protagonist to protect her sister's safety. In the end, the female lead jumped off the cliff because she had forgotten why. However, she survived the disaster (the second book said that she was not actually dead), but she fell in many places and was disfigured. He remembered that the female protagonist had a good friend who was very good at martial arts and kept calling him a weirdo. Sigh, I only remember these…The name of the Sincere Help Book!