The two lines in this excerpt tht reflect those themes are:
"To make us wish that we were in his place. "
This line explains perfecty the mentality of “the grass is greener on the other side”. Because its explicitly saying "we" are wishing to be in someone else place, meaning people are never satisfied with their own situation; they always think others have it better.
"Went home and put a bullet through his head."
This phrase makes reference to the theme of dissatisfaction.