Lyric discussion by dross 

Cover art for Rocket lyrics by Smashing Pumpkins, The

I miss me I miss everything I'll never be

These two lines sum up the whole meaning of the song.

Billy wrote this song about a time machine that was shaped like a rocket.

It was in this time rocket that Billy was able to view and meet his possible future selves.

Billy became great friends with some of his future Billy's—the one that ended up marrying Courtney Love, for instance.

This is why he says that he misses himself and misses who he'll never be. Eventually he had to ultimately decide on one future path and stick to it.