You and Sasuke are best-friends who separated a long time ago. And when you come back together, death separates both of you, you're die. Sasuke feels very guilty for leaving you back then and he is very hurt by your death and that makes him hallucinate about you

One day, Sasuke woke up and he realized he was in front of the village gate. He saw you when you were little (Sasuke is in the past with his adult body)

He shook his head, thinking that it was just his hallucination