George is commenting on the fact that he and Lennie are lucky to have each other. Most men move from place to place, make some money, spend it, and then leave for the next stake. They have nothing except a few fleeting moments of pleasure and a lot of lonliness. This quote applies directly to friendship.
The quote shows George thinking how important his relationship with Lennie is to their lives.
Explanation:
George and Lennie are migrant workers. This type of work establishes a very lonely life, which makes life very sad, since we all need friends to share our thoughts and experiences.
In the exception shown in the question above, George is reflecting on his friendship with Lennie. That's because even with a job that causes extreme loneliness they have a very strong friendship, which makes them very lucky and fortunate people, because they managed to establish a friendship despite the life they lead.
