Let's list what we know about the speaker.
It's that last one we're interested in. This guy is so sad that he can't imagine any good or happiness in the future. He's so overwhelmed by grief that he's driven to speak in crazy hyperboles. It's as if his sadness has completely changed the way he sees the world around him, and he wants that sadness to be reflected back to him by everything he sees. It's serious business. But the problem is, he exaggerates so consistently that we may even have trouble taking him seriously sometimes.
And that's a bummer, because we believe that this guy is deadly serious. The mourning here is palpable, and it's no wonder this poem has become so popular at funerals and memorials. Anyone can relate to this speaker's consuming sorrow. We've been there, buddy.