To begin, the story's setting is very dark and depressing. The neighborhood is portrayed as one that is constricting. The homes are dark and close together, for example. Immediately, then, the setting affects the dark mood of the story.
The references to blindness become very important and apparent by the end of the story. The narrator has been blind to what he has been doing (wasting time fawning over a girl, and one he will never be able to have, at that) until the end of the story, when he has his epiphany (or moment of enlightenment or realization). He realizes that he has fallen victim to grandeur visions of love and that he has neglected all other aspects of his life in order to pursue his crush. Many times when people are not aware of things they are doing, they can be said to be "in the dark," so this is relevant to the blindness/darkness, as well.