In the first stanza, the speaker says that his friends have forsaken him "like a memory lost," that his woes "rise and vanish ... / Like shadows in love's frenzied stifled throes." These are both similes in which he compares himself and his feelings to objects which are insubstantial, intangible. A simile is a comparison of two unalike things where one is said to be "like" or "as" something else. These comparisons help to show how he is treated, as something which is barely present or whose presence has no meaning or importance, rather than as an actual, living, breathing person who has value and worth. He says that he is, that he does live, but that he is

... like vapours tossed
Into the nothingness of scorn and noise,
Into the living sea of waking dreams ...

The simile, in which the speaker compares himself to water vapor—again, something insubstantial—is followed by a metaphor which seems to compare the rest of the world to a living sea, something a great deal more substantial than he. A metaphor is a comparison of two unalike things in which one thing is said to be the other. These comparisons—the speaker is merely vapor and the rest of the world is an ocean—show how insignificant he is made to feel by the rest of the world, which has, for some reason, written him off. He also compares the things he loved best in life, via metaphor, to a "vast shipwreck." Thus, he wishes that he could go somewhere else, someplace where there are no other people, so that he could live with God and sleep as peacefully as he did in childhood.