No man is an island… unless he's an itinerant worker during the Great Depression, and then he's about as lonely as you can get. But for all the talk about loneliness in Of Mice and Men, these guys sure do hang out together a lot. (They even go to the whorehouse together. We bet they visit the bathroom at the same time, too.) Does this mean they're not isolated? Or do they meet, make new friends, new enemies, and then head out to their next job, all the while failing to make any real, human connections?
In Of Mice and Men, isolation is safer than togetherness.
Because they are together, George and Lennie are never truly isolated, no matter how different they may be.