Of Mice and Men is the equivalent of a bro hug: all sublimated emotion, gruff affection, and hearty back pats. George and Lennie don't text each other eleven times a day, and they don't like every single cat picture the other posts on Facebook—but we still get the sense that they take their friendship more seriously than anything. After all, what else do they have? And what else do any of us have?
In Of Mice and Men, friendship is dangerous: every time any character gets close to any other, something goes wrong.
George sees friendship as a practical relationship as much as an emotional one. Friends do difficult things for each other—like killing.