Which line(s) of "The Raven" indicate the narrator’s loneliness?

There are several lines in "The Raven" that contribute to our perception of the narrator's loneliness. In the second stanza, he discusses wishing for "the morrow" because he had, in vain, sought an end—however temporary—to his sorrow over his "lost Lenore"; thus, we know that this night feels as though it will never end because the narrator is grieving his beloved (lines 9, 10). If he had another person with whom to pass this time,...

There are several lines in "The Raven" that contribute to our perception of the narrator's loneliness. In the second stanza, he discusses wishing for "the morrow" because he had, in vain, sought an end—however temporary—to his sorrow over his "lost Lenore"; thus, we know that this night feels as though it will never end because the narrator is grieving his beloved (lines 9, 10). If he had another person with whom to pass this time, he would not need to turn to his books as a distraction. 

Then, in the tenth stanza, the narrator considers the raven which has flown into his room, saying, "'Other friends have flown before— / On the morrow he will leave me, as my hopes have flown before" (58-59). In other words, the narrator anticipates this bird abandoning him just as everyone else has apparently abandoned him up until now, including Lenore. These lines show just how lonely our narrator is, so lonely that he assumes even this bird will not remain with him because no one else has.

Finally, in the seventeenth stanza, the narrator implores the raven to "'Leave [his] loneliness unbroken!'" (100). This is the most explicit piece of evidence that the narrator feels an intense loneliness.