How are Lennie and George diametrically alike in "Of Mice and Men"?
I have a problem with the word "diametrically" since it suggests contrast rather than similarity.
Lenny and George have one thing in common which "binds" them - they have known each other since childhood are are not lone drifters as other migrant workers. The fact that they have each other to count on for companionship distinguishes them from the other workers, who are true loners. For this reason they don't suffer as much from loneliness and alienation as they would have otherwise.
Lennie and George are different in that Lennie is dependent upon George as a caretaker, whereas George often wants to escape from his responsiblity towards Lenny. This parent-child symbiosis is not always a healthy one, but it is necessary for Lennie's survival in a world too difficult for him to tackle alone.
This interdependence is the main reason George decides to shoot Lennie in the end. He cannot imagine Lennie's life being worthwhile if he is delivered into the hands of strangers as a criminal. His shooting Lennie is his way of sparing him from an existence too cruel to bear.