This song always reminded me of Shakespeare's Romeo and Juliet
The themes fit perfectly. Romeo and Juliet cannot be "with" each other because of their feuding families, but they cannot be "without" each other because they are so in love. Hence, "I can't live with or without you."
The extra verse sung in the live version makes the comparison even more relevant. It sums up the entire idea of Romeo and Juliet.
"We'll shine like stars in the summer night,
We'll shine like stars in the winter night.
One heart, one hope, one love,
With or without you."
In the Slane DVD, there is even a star chart on the giant screen behind the band. Stars are a recurring motif throughout the play.
"Two of the fairest stars in all the heaven,
Having some business, do entreat her eyes
To twinkle in their spheres till they return.
What if her eyes were there, they in her head?
The brightness of her cheek would shame those stars
As daylight doth a lamp."
"Come gentle night; come, loving black-browed night,
Give me my Romeo, and when I shall die,
Take him and cut him out in little stars,
And he will make the face of heaven so fine
That all the world will be in love with night
And pay no worship to the garish sun."
-Juliet, III.ii. 21-27