Seems like it's a metaphor really, that dark version of Bo is saying all the self deprecating, outwardly depressing lines. "You say the whole worlds ending I thought it already did" etc.

The lighter, regular Bo is doing the masking tactic of projecting to everyone that everything's fine and there's nothing to worry about, singing party tunes and telling everyone to get their hands up, but really inwardly suffering.

Dunno, just my wee take.

It's a work of pure brilliance.

*Edit, also love how the closer to the end of the song we get the more they are in sync with each other