Lyric discussion by aliciasaidso 

Cover art for Get Big lyrics by Okkervil River

I think it is about him loving this girl, but needs to let her go to let her grow.

"And I can't say why each day doesn't quite fit the space we saved for it."

she is drifting away and they arent spending the time together they/he hoped they would because she is too busy partying and doing whatever

"So drink your cup down to the dregs and leave that club shaking legs with another guy, but just remember: I'm not him."