I think these lyrics are written vague on purpose, to keep them broadly relatable, and thus any intepretation based on the dark mood must be true. But in my view they evolve around the exsistential numbness and ways of coping, in this case the desperate love. It seems that just as he is trying to loose himself in this girl, she is trying to loose herself in drugs. And both of them is running from a reality that is somehow less than they imagined - she is fucking for a living and his fame is hollow. They both wanted and deserved better but thats just how it went, and the lyrics is refreshingly unsentimental. It does not seem to be the drugs thats the problem, its that they are never enought, meaning that the real issue is lying untouched underneath. I think this relates perfectly well to the theme in "swim good", the fight for staying over water in a sea with no percievable end.
In that way they can relate to the generation thats just now trying to enter the adult world and jobmarked. The fight for finding a place to stay, and the nessesity to give up dreams to stay alive. The fact that we never got the world that we were promised.
And, btw, sorry about the language - english is not my native tounge.