This whole album is full of sparse and emotional piano-driven gems, which allows Spencer Krug's (Wolf Parade, Sunset Rubdown, Swan Lake) brittle poetry to really shine through.
This song is steeped in sadness, and to me really just epitomizes the full breakdown of love. The sort that not only destroys a relationship, but also eviscerates your image of self, but also how you interact with your physical reality, and necessitates some introspection and growth in order to pick up the pieces.
Love is sort of like light. It needs darkness in order to exist and be appreciated, and I don't think you can really appreciate the highs of the feeling until you've sunk to the depths of its absence. In fact, I think the absence is still love. Love can have a negative or a positive existence, but it's all love, and all part of celebrating the human experience.
(There's also a full-band version of this song that is equally good, but in a different ways)