Disclaimer: When N says "saying split personality or bipolar" would have made more sense, as an alternative to Bella calling Edward someone with a "multiple personality disorder", it is just a remark on what an angsty teen in early 2000's would have said---it being a common part of a teen's vernacular. The comment was not said to mock or be insensitive towards anybody who suffers from these disorders. The same goes for the trauma attachment styles discussed as well.