I take this song as finding a person who is ignored and left alone because of either being bullied or some other reason, and making friends with that person. All of your friends then leave you (likely because they were fake friends/the ones bullying the person) because you made friends with the person. And so you begin to get bullied too. You think that that person will leave you because you’re the one being bullied now (referring to “but what if i run out of fertilizer”, “what if the clouds run out of rain”, etc.) but you got a lifelong friend (as the ending lyrics imply) who won’t leave your side. You end up realizing that, and thus you never leave each other’s side.
I take this song as finding a person who is ignored and left alone because of either being bullied or some other reason, and making friends with that person. All of your friends then leave you (likely because they were fake friends/the ones bullying the person) because you made friends with the person. And so you begin to get bullied too. You think that that person will leave you because you’re the one being bullied now (referring to “but what if i run out of fertilizer”, “what if the clouds run out of rain”, etc.) but you got a lifelong friend (as the ending lyrics imply) who won’t leave your side. You end up realizing that, and thus you never leave each other’s side.