As kiwifarms isn't a hivemind I want to pushback on the idea of the demonic posession of Nick. I could argue that as an atheist there are no demons or souls thus no demonic possessions. But I'd like to take a more nuanced position. Nick is acting the way he is because he beleives he is possessed and thus has 'permission' to do whatever he wants. Nick has stated some bizzare occult-adjacent opinions/views towards his Christian faith, gods a sinner, jesus was a sinner and also not real. So for Nick I think he beleives these things because thats a tool he needs his to remove the psychological control/guidance his faith via his upbringing has placed on him. He wants to do all the drugs anf fuck whoever and cares about no one but himself. To justify this desire with what is expected of him via his faith he starts beleving in the occult and demon possession or whatever. It may sound strange but people act and think in strange ways to prevent and minimise cognitive dissonance all the time, this is compunded by Nick being a massive narc.
tl;dr Nicks not demonically possessed but he's allowed himself to beleive in that idea or something akin to it to justify his utterly selfish actions becuase hes utterly selfish and self destructive.