Sadness comes from the wish for happiness.

The heart is sad and full of sorrow, and I can do nothing,
to help you feel life's worth living, you know I would do anything. But I, I am just a man and you, you bring me to my knees. And I, I'm living in a winter, and you, you are my summer breeze.

The heart is sad and full of sorrow and all I have are memories, when times are good and full of loving there no  need for such reveries.  But I, I am just a man. And you, you are my everything.  And I, I am a lock without keys.
And you, you lift me from my knees.