"
And I just hope you know,
That if you say, (If you say)
Good-bye today, (Good-bye today)
I'd ask you to be true (I'd ask you to be true)
Cause the hardest part of this,
Is leaving you
He wants her to know that if they leave each other, that he wants her to only ever love him, and know that he only ever loved her. When someone stays true to someone else, it means that they will never fall in love with another.