When and because

When you have him, don't make him your everything.
Don't make him the stars in your dark sky,
Don't make him the air you breathe,
Don't make him out to be the only reason for your smile.

Because if he leaves you, you'll be left with nothing.
Your sky will be dark,
You'll suffocate,
And the only one who can put a smile on your face has taken it and walked away.

But my sky is dark, and i suffocate.