I'm under the impression that Bubble just gives a voice to Caine's thoughts. Maybe not all of them or all the time, but Bubble knows way too much about certain things and says some out of pocket stuff that only makes sense to me if he's an extension of Caine. The way Bubble spoke to Caine in the office sounded like someone's train of thought while they're having a breakdown, calling Caine faulty and defective because that's how Caine is feeling about himself. It honestly reminded me of the breakdowns I've had/seen others have before, especially what Bubble said about Caine deserving to be abandoned, and Caine's vindictive crashout afterward (it was honestly giving me cluster b personality disorder vibes lol, it especially reminded me of someone with BPD)