I see this poem as presenting hope disguised in despair. In a literal sense, the poem is talking about the despair one feels after losing a lover. However, hiding behind the despair is hope. This hidden twist can be inferred by the choice of the poet's metaphor: the sun, which traditionally represents hope, life, regrowth. Just as the sun will come out again tomorrow and light the Earth with its quality of sight, so will the personas hope to again find love. Furthermore, the setting of the sun allows for the Earth to rest and recover from the activities of its day, allowing it to have grown stronger the following day. In parallel, the persona will need some time to recover from his loss and grow stronger from his experience to face a brand new love. In essence, the poem states that there is more than one true love in life.