Curly was at the same bar Slim and George were. George is drunk and exposes himself how Lennie is dead because he killed him.
Curly wanted revenge on the death of his wife so he took Lennie's body and buried it by the river.
Curly makes George work extra hard so hes farther away from leaving the ranch. George is exhausted and tired of working for Curly but he knows his goals are too valuable to give up on.
George leaves the ranch and buys his own, he eventually marries a smart woman. He was happy but still felt empty inside. He felt saddened by Lennie's absence.
The evil deed he did to Lennie is haunting his soul and can't continue his life smoothly. He thinks about his life and how he's achieved his and Lennie's goals but Lennie is the one missing out of his life.
George one day goes to the bush where Lennie and him had a designated spot. He discovers Lennie's body is buried there and he digs it out and all the people who knew Lennie end up connecting the dots.