What was the narrator's relation to Roderick Usher?
The narrator in Poe's "The Fall of the House of Usher" has known Roderick since they were boys. He says
Roderick Usher had been one of my boon companions in boyhood ; but many years had elapsed since our last meeting. A letter, however, had lately reached me in a distant part of the country - a letter from him - which, in its wildly importunate nature, had admitted of no other than a personal reply.
The narrator travels to the Usher home and is immediately disturbed by the appearance of the house, which is in itself a character in its own right. Even though the narrator is tempted to leave, he remembers that Roderick
. . . spoke of acute bodily illness - of a mental disorder which oppressed him - and of an earnest desire to see me, as his best, and indeed his only personal friend, with a view of attempting, by the cheerfulness of my society, some alleviation of his malady.
This "bodily illness" turns out to be hyperesthesia, which is a severe acuteness of the senses; and hypochondria, which is an irrational belief that one is sick. This hypochondria is so intense in Roderick that it becomes self-fulfilling. Even though the narrator feels uncomfortable in the presence of his friend and his house, he remains because he knows Roderick truly has no one else.