The song isn't simply about his relationship. He's dreaming these things "Last night's dream..." and he wants to keep sleeping so he can dream about the relationship some more
"I'll keep sleeping
If I don't stop dreaming
I would stop my breathing for you
I'm not leaving
This life I'm dreaming
'Cause I can't stop living with you"
So he's living a relationship in his dreams essentially.
The song isn't simply about his relationship. He's dreaming these things "Last night's dream..." and he wants to keep sleeping so he can dream about the relationship some more "I'll keep sleeping If I don't stop dreaming I would stop my breathing for you I'm not leaving This life I'm dreaming 'Cause I can't stop living with you"
So he's living a relationship in his dreams essentially.