Jesus people, stop freaking out about this song
It's something new, and different
...
Quite honestly, I believe this song is about taking love for granted, and then losing that love. They had "too much" love and "too much" time, so they figured that "tomorrow was promised" when it wasn't. It's like the philosophy that one should live like they're dying--they don't know what will happen tomorrow, so they should live life to the fullest.
It seems like this song is about someone who had too much time, took it for granted, and now has regrets, possibly because his love is gone.
Like another user said, it may have something to do with the need for personal space, but I personally believe that more of the lyrics point to a surreal, "How did I end up here" feeling, as if you'd lost your love and your life is in shambles.