The song is not about leaving someone behind, it's about his life, touring, on the road, and how that life had trashed a relationship. The phrase about “Don't know when I'll be back again!” is not literal, it's how he feels starting an extended tour. It's a sad song, and well done.

by John Denver John Denver wrote and recorded “Leaving on a Jet Plane” in 1966, when he was just 23 years old. It was included on his debut demo recording as “Babe, I Hate to Go.” He made copies and gave them to friends as Christmas presents that year.