I think he is borderline and also somewhat histrionic, because his public proclamations of love for you appear histrionic, and his saying that you were a perfect gf appears both borderline and histrionic.

Whatever it is, his case is really complex and it is good that he is not your problem now (I commend you both for feeling enough compassion for this new woman to want to reach out and for your self-restraint - she will have to figure this one out on her own). A change in dialect that you picked up on... it is almost as if he had two personas. A dialect is usually a very stable characteristic of an adult. To change that... mysterious, I would say.