Working backwards, chapter 3 ends with the idea of Lennie feeling loneliness if he is denied the opportunity to tend the rabbits. Despite the fact that he broke Curley's hand and that he has instigated the elements that will lead to his demise, Lennie feels a sense of loneliness if he is not able to tend the rabbits. It is for this reason he pleads with George so that he is not inevitably feeling alone and apart from his true love.
Curley experiences loneliness in how everyone else in the bunkhouse has seen him effectively beaten by Lennie. There is a loneliness that he displays, even though he is amongst everyone else. His claim to fame was that he could "lick anyone." Lennie effectively disproved that and, in the process, Curley feels extremely alone as a result. As George talks to Slim, he explains the reason he befriended Lennie was to escape his own sense of loneliness as a migrant worker:
I ain’t got no people. . . . I seen the guys that go around on the ranches alone. That ain’t no good. They don’t have no fun. After a long time they get mean. They get wantin’ to fight all the time.
While Lennie might be a nuisance to George, he is the reason that George is able to escape his condition of loneliness. Certainly, Candy feels alone now that his dog has been shot. Candy feels this sense of loneliness in the "silence" that Steinbeck continually raises in the chapter. Candy's dog experiences his own loneliness in those fateful last moments before Carlson's luger silenced him for good. The result is that Candy's loneliness compels him to latch on to the dream that Lennie and George share, reflecting a discomfort with his condition of loneliness.