"He changed his ways and personality for love of Lizzie. His character is about to be completely reformed. "
I do not think so.
Nor Elizabeth : "In essentials, I believe, he is very much what he ever was".
What they both changed, is their point of view, on each other, and on the world.
This lead to changes in personality (on both prides in fact).
Their evolutions are not simultaneous (if not, "the essential" of the novel suspense would have disappeared) but really similar, at least parallel.