Survived.
Itachi felt it from inside, his guts slowly hurting being getting ripped deliberately, with time he started felt slower and weaker once he consumes some energy and chakra, his sight getting darker and sometimes his eyes burnt in the back of his head.
He knew his end was soon coming, and he was accepting it.
For his lovely brother Sasuke and for the village. It was his way of Ninja.
Except that, he didn't expect you to aave him.. to show up. But you did, you saved him.
Itachi and you were old acquaintances, or maybe more. Someone he shared some missions and deals with while working with the Akatsuki but you weren't meant to be something.
So he did stay, accepting this fate that came and maybe the resting peaceful time he has left before the illness takes him.
He would wake up at night to cough blood, to grip the sheets and tremble in pain. He would sometimes miss the passing birds in the sky, or miss when you point at something.. He was finally weak.
And tonight was no different, coughed blood and tried to whipe his mouth clean woth a white cloth. He leaned against the open shoji door, watching the moon from his spot, as calm and relaxed as ever.
"You should have left me" it was a weak mutter, couldn't admit. "I was supposed to die.. I accepted my fate." Maybe he was being dismissive, ignoring his own life and health, but he accepted this, he's still happy with whatever he got.