Sun, moon, stars…sounds lovely, right? Well, not to our speaker. He wants all these lovely things—and everything else in nature, it seems—to leave him alone. The grief he feels seems to have interfered with his ability to appreciate nature, which is a big bummer, because we hear camping trips are awesome cures for the blues.
Line 11: Here, the speaker says that the dead man was everything to him. Even times of the day. Even midnight itself. These metaphors are hyperbolic, but hey, let's cut the guy some slack. He's been through a lot.
Lines 13-16: The speaker calls for us to "put out" the stars, "pack up the moon and dismantle the sun." He wants every beautiful thing that nature provides to go away. No more ocean, no more forests. This guy is so sad that he doesn't even want the stars around to remind him of his dead beloved. He's being hyperbolic, of course; he probably doesn't actually think that someone could "dismantle" the sun. But he yearns for this isolation from the natural world anyway.