After discussing the poem "Bright Star" by John Keats several times here, and having been studying it for Poetry Out Loud, I think it deserves a complete analysis.
What I see when I look at the poem, is the narrating voice, likely Keats, to be first introducing the idea of eternity and consistency in comparison to a star. He wishes to be as "steadfast as thou art," speaking directly to the star. However, he then dismisses all other qualities of the star, not alone, looking from above onto the world below as sleepless creature, something that no human could ever be.
No, this star is unreal to us. "No--yet still stedfast, still unchangeable-- Pillow'd upon my fair love's ripening breast," says lines 9-10. What is truly being asked is for the constant nature the star possesses, the eternity it gets to live. Contrasting with the star is the impermanence of life, the "ripening breast" implying change and movement of humans not seen in the lines preceding it in reference to the star.
The eternity being asked for is not the infinite time a star experiences, but a forever of love and passion on Earth. Only in the final line does Keats accept the possibility of dying in pleasure over living in harmony forever.
The poem asks for the lifetime of a star, yet the narrator cannot relate to what the star is, in itself. He is asking for something entirely inhuman and impossible. Keats struggles to cope with the rush of time on Earth as human, when stars existing above Earth live forever. In the final line, he says he will go willingly if he can die in love if he cannot exist forever. Keats died away from his love, Fanny Brawne, at the age of 25 in Rome, Italy.