Y'all are so juvenile-
He obvi means that he is jealous of her nature and loves it about her, but also resents that he himself isn't like that. So he may come to hate that about her not because of what she has but what he is lacking! Or something along those lines idk yet but we're probably going to get to the specifics of what he means.
Oh wow, a complicated character that is capable of feeling more than one thing? I know that these kinds of romance stories tend to be geared towards young women and can be a little simplified for the sake of cute romance and sweet fluff but it shouldn't be that hard to figure out that there's more to his feelings than the use of one word.