George and Lennie, in Of Mice and Men, differ greatly in regards to the way that they interact with those around them.
The most poignant example would be the "relationship" between Curley's wife and both Lennie and George. George tells Lennie not to have anything to do with Curley's wife given she is a "tart". George tells Lennie, "Don't you even take a look at that bitch. I don't care what she says and what she does. You leave her be."
Even with this threat, Lennie does not "leave her be". Instead, he is enamoured with her because of the way that she feels- he loves soft things.
Another example where Lennie acts differently with others than George would is when Lennie enters into Crooks' bunk-room. Crooks tells Lennie that he has no right to be in there. George would have left- Lennie simply does not know any better. He seems to believe that all others are his friends.
Lennie is trusting of all people around him, even given the warnings from George. Unfortunatley, this leads to Lennie's downfall. George simply knows better than to be trusting of others and presents himself as a guarded man.