I have no doubt that he hates her, really, deep down but like you said, he's always going to have that side of him that isn't filled with good because of what she did to him.

it would be all too easy for that hate to become something else and easier for her to get to him if she plays on his fears; of guilt, maybe, and of being the one that's always going to walk the line between good and evil.

(especially with peter not around to convince him otherwise)

lucy's there but it was always peter that edmund needed the approval from; peter that edmund wanted to make proud, at least in the end. (it was always about peter in caspian - even when it should have been about caspian)

and now peter's not there and it's just lucy and jadis is going to so tempting for him.