Question: Why did Catherine change her mind about killing Nick at the end? Obviously she was planning on killing him anyway, but she changed her mind only hours after ending their relationship when her book was finished and was of no further use. So why did she spare him? Was it because she fell in "love" with him?
Question: Did Stone have a motive for all that she did or was she nuts and doing it all for fun?
Answer: I would say her motive mostly amounts to exploiting others and real-life stories to create more fascinating and complex stories to satisfy her insatiable ego, whether she chooses to kill them or not in the story.
Question: Why did Catherine target Nick? I know he's a big douchebag, but that can't be the only reason right? Was it to get revenge against Beth for once and all for leaving her?
Answer: No definitive answer is given in the film. Catherine didn't need a reason for anything that she did. As for Beth, that was just a bonus, or a coincidence. It could be argued that Catherine targeted Beth, and Nick was just unfortunate to be involved with Beth.
Answer: Because she's insane? And very ill. And dangerous. A pure bred psychopath. She got off screwing with him, his head. She has a degree in effing with you. Beth was just a bonus. Unlucky. Collateral damage. Unfortunate. Catherine was, is a clinical psychopath. She had no reason. Or it was fun for her. She was one twisted broad. An evil dame. (IMHO).
Answer: There's no definitive answer to this and the ending is deliberately ambiguous and open to interpretation. The audience is left to speculate whether or not Catherine kills Nick, or if she intended to kill him but changes her mind because she loves him, or intends to kill him at a much later time, and so on.
raywest ★