What was killing Itachi?
The fight with Sasuke caused him to hasten his death from his illness because he used too much chakra and this is what caused him to die in the end. Using Susano killed him.
Was Itachi really sick?
Yes, Itachi did have a disease. Itachi’s sickness was not introduced until late into the story. It was implied during his fight with Sasuke that his issues were related to overuse of the Mangekyo Sharingan. However, the later clarification of his illness causing impending doom implies its unrelated to jutsu.
Why did the Creator killed Itachi?
Kishimoto also said in the interview that he only killed Itachi off, because otherwise he would have defeated Madara. He seeks out Orochimaru in order to become powerful enough to slay Itachi and seek vengeance for his clan.
Was Itachi blind while fighting Sasuke?
yes he was blind ( not complete) and suffering was some unknown illness.
Why Itachi got his arm like that?
With Itachi, it has been speculated about his illness. It is reportedly a respiratory illness but there have also been other diagnoses that have speculated that due to the pain that he was in, especially that particular arm, he would rest it in the front of his Cloak to ease the pain.
Who killed Akatsuki members?
Saori : killed by chiyo.
Who killed Black zetsu?
He was killed by an Amaterasu infused Susanoo arrow that incinerated him. Black Zetsu was actually a physical manifestation of Kaguya’s will-making him hundreds of years old. During the war he fought the Mizukage and Naruto and managed to survive, and he even managed to overpower a god-tier Madara to resurrect Kaguya.