Mr Banner teaches Bella and Edward Cullen's Biology class, apparently feeling that they're so dumb they need to cover subjects like mitosis which most schools learn in seventh grade. Like every other male in the Twilight series (excluding Charlie and Billy Black, whose interests lie elsewhere), he wants Bella's jailbait booty, because if there was a single character who didn't she wouldn't be speshul enough. That's not totally sick and wrong. There's nothing wrong with pedophilia (if you live in Meyerland that is).