Okay so it already ended,but did I skip sumthing or what because I didn't saw Muzan's back...

His backstory is already told a long time ago but i forgot which chapter, he was sick for so long, his parents asked for a doctor to cure muzan, but muzan was not cured, someday muzan got mad and lost his trust to his doctor and end up killing his doctor and his parents too, but long after that he realized that his doctor wasn't lying about keeping muzan alive, correct me if i'm wrong tho