Knowing that this song is set in 2020 sure does make "'til my friends come home for Christmas" come off differently.

Different *how*, I'm not entirely sure. It could be this, or it could be intended as more of a "the war will be over by Christmas" vibe where actually he's going to be stewing alone for years. (But given that he'd apparently been fully expecting his girlfriend(?) to visit him, I'm leaning towards the former.)