How do Ponyboy's relationships with Darry and Sodapop differ?

Pony is very close to Soda, he is the brother that Pony can relate to in a brotherly fashion. Ponyboy's relationship with Darry is difficult and conflicted. Rather than simply getting to be the "big" brother, Darry has to play mom and dad, as well. Thus, Pony feels as if Darry is always unhappy or disappointed in him.