Hey, thank you for playing. There is a major bug in the game where when you beat the final boss the game breaks. It is supposed to show a cutscene (my favorite cutscene BTW) but unfortunate I can upload the fix until after the game jam.
As for the gravity nodes, those operate similar to the mouse. You need them to maneuver the comet (I'm actually shocked you only used the mouse) and unlike the mouse which has a limited duration per level, those cannot run out. Not all of them are useful though, so you have to discern when and which to turn on/off.