Backwards Down the Number Line

"Happy Happy, Oh my friend"
Blow out candles once again
Leave the presents all inside
Take my hand and let's take a ride

Backwards down the number line
You were eight and I was nine
Do you know what happened then?
Do you know why we're still friends?

Laughing all these many years
We've pushed through hardships, tasted tears
We made a promise one to keep
I can still recite it in my sleep

Every time a birthday comes
Call your friend and sing a song,
Or whisper it in to his ears,
Or write it down, just don't miss a year

You decide what it contains
How long it goes
But this remains
The only rule is it begins
"Happy Happy, Oh my friend"