We sure love sleep, but not the kind of sleep in this poem. That's because the "sleep" in this poem isn't your typical nightly snooze, but the permanent sleep of death. The speaker is tired of his life: he's been abandoned, and everything he once loved is gone. He wants to die, but he sees death as a peaceful sleep, an escape or release from what is a very unhappy life.
Line 7: Well, there's no mention of sleep here, but we do have a "living sea of waking dreams." If the speaker is having "dreams," even if they are "waking" ones, he's still sleeping in some way. Sleep equals death in this poem, so the speaker is already sort of dead. That "living sea" is also a metaphor for the way the speaker perceives the hustle and bustle—the "scorn and noise" (7)—that surrounds him.
Line 16: The speaker isn't talking about taking a nap, so sleep is a metaphor for death. That phrase "sweetly slept" is pretty neat. It's also an example of alliteration!