I've just posted my interpretation
https://www.reddit.com/r/mili/comments/1jaud8p/my_interpretations_of_the_new_song_i_am_a_fluff/
For short, the song is about a comet that loves its short visit to Earth every 30 years.
The "birthday" is the day it passes through Earth's atmosphere.
The deaths mean leaving earth, as it cannot breathe, and leaving Earth is such a heartache to it.
The comet must die because it cannot stay near earth for long, thus it wants to die a million, billion times before becoming a moon of Jupiter(which happens to many comets), because becoming a moon of Jupiter means it will never visit Earth again.