The question states that "Richard Cory" explores that "the grass is greener on the other side" affects all humans.
Because of this, I believe the answer is B and D.
With B and D, you can see both sides, both people from opposite sides of "the grass" who wish to be on the other side.
B. "To make us wish that we were in his place" says this directly, while D. "Went home and put a bullet through his head" implies it. He was obviously unhappy with his life, and wished for something else.
I know I'm late, but I hope this can still help someone.