At the beginning of the chapter, Ralph's frustration is focused on the shelters and the boys' inability to build anything substantial. He has tried to organize the boys to build, keep the fire going, etc. But their progress is minimal. When Jack returns, Ralph's frustration only grows since Jack hasn't been successful either. Despite drawing off a group of capable boys to hunt with him, they haven't brought back any meat for the group.
Ralph feels this frustration more than the others because he sees himself as the leader and feels very strongly the desire to bring back some of the trappings of civilization. He is attached to the fire as their means to a rescue and attached to organization as a way to avoid further deaths like the boy with the birthmark.
As he and Jack begin to drift further apart, Jack finds a freedom in his desire to become more savage whereas Ralph seems to find only frustration at his inability to make things go right.