From their NPR interview: http://www.npr.org/blogs/therecord/2014/10/09/340115612/the-pop-punks-of-anarchy
" part of what we were trying to do with the lyrics of that song was convey something about the exasperation of loneliness and romance. How, when you're quite an anxious, neurotic, nerdy person who spends a lot of time ruminating on just about everything, there's a temptation to think, re-think, over-think stuff until the cows come home in search of a way to properly, precisely and accurately articulate your feelings. But time and time again, the words that seem to convey things best of all, are the ones that you started with. The simplest, bluntest, "naïveté" sounding words of all, like "I Miss You, I'm Lonely." Those are Daniel's lines actually, we wrote it together, and he liked the idea of having something really basic and simple and honest as the lyrical hook, then writing this hyper-literate song around it."