Hello there! >o<~!
Answer: George kills Lennie to spare him from a painful death at the hands of the mob. When the men on the farm discover that Lennie has killed Curley’s wife, they set out to find him. George knows Curley will not care that Lennie’s actions were unintentional and decides to give Lennie a quick and merciful death to spare him from the suffering he would endure if left to Curley and the other farmhands.
Hope this answer your question! If I forgot something please tell me!
:)