Rod McKuen wrote Seasons in the Sun, Jacques Brel wrote the music. The lyrics in the link above are the watered down version that Terry Jacks did for popular release. I remember reading that McKuen hated it (and may not have even authorized the changed lyrics) but the info wasn't on any of my albums and it was years ago, so I can't be sure. The original lyrics are as follows:

SEASONS IN THE SUN
Rod McKuen, Jacques Brel

Adieu, Emile, my trusted friend
We've known each other since we were nine or ten
Together we climbed hills and trees
Learned of love and ABC's
Skinned our hearts and skinned our knees
Adieu, Emile, it's hard to die
When all the birds are singing in the sky
Now that the spring is in the air
Pretty girls are everywhere
Wish for me and I'll be there
We had joy, we had fun
We had seasons in the sun
But the wine and the song
Like the seasons have all gone

Adieu, Papa, please pray for me
I was the black sheep of the family
You tried to teach me right from wrong
Too much wine and too much song
Wonder how I got along
Adieu, Papa, it's hard to die
When all the birds are singing in the sky
Now that the spring is in the air
Little children everywhere
Think of me and I'll be there
We had joy, we had fun
We had seasons in the sun
But the song and the rhyme
Were just seasons out of time

Goodbye, Françoise, my faithful wife
Without you I'd have had a lonely life
You cheated lots of time but then
I forgave you in the end
For your lover was my friend
Goodbye, Françoise, it's hard to die
When all the birds are singing in the sky
Now that the spring is in the air
With your lovers everywhere
Just be careful, I'll be there
We had joy, we had fun
We had seasons in the sun
But the stars we could reach
Were just starfish on the beach

We had joy, we had fun
We had seasons in the sun
But the wine and the song
Like the seasons have all gone
All our lives we had fun
We had seasons in the sun
But the stars we could reach
Were just starfish on the beach

The two versions are similar, except for the final verse. (You probably can tell that I prefer McKuen's.) Hope this helps.