He didn't always hate her. When he first met her, he merely disliked her, like he disliked everyone else. Even the fact that her army was better than his (Phoenix, Rabbit) didn't make him hate her, and he really didn't talk to her, anyway - she was younger.
Then she was in Rabbit and he was in Condor, and he still didn't hate her.
Then she was in Flame and he was still in Condor, and even though her commander was among the best and her comrades among the best, he didn't hate her.

When Yeager told her his nickname in Condor, then he hated her (and Yeager, but he'd hated Yeager since he was transferred into Condor). And he hated arguing with her, and he hated that she found out that he'd thrown up a few times after arguing, and he hated the throwing up, too. (He especially hated the throwing up.)

And then he got command, and he still hated her, because he'd gotten used to it by then, but he was too busy hating his army for not being perfect. He won his first two battles, and he'd subsided to neutrality about some of his soldiers, but then he lost his third - and he went back to hating them and never stopped.

He came home for a week and found that his parents had gotten divorced, and his mother treated him like he was still six. He went to Support and he was too busy to remember anyone from Battle School, least of all to hate them - there were plenty of people to dislike and hate at Support School, and not that many to be neutral about.

He was in third year, on Green Team, when she showed up again. He was surprised enough to forget he hated her, until she called, "Funny seeing you here, NG, they haven't iced you yet?" at breakfast the next day.

And he hated her and he hated himself and he yelled back, "That's Cadet McGarvey to you!" And the other Greens started calling him NG - and NDG, once they'd figured out what the N and the G stood for - and he hated all of them, even the ones he was neutral towards.

He asked for a transfer and was put in Indigo, but Indigo was where she was, and the teachers wouldn't transfer him again. After a few weeks, though, he began to find it comfortable, even relaxing to hate her, and he found that he didn't even dislike some of the Indigos, even though they called him NDG and didn't save him a place to sit in the mess.

And one day they were arguing in the corridor and something in his eyes must have scared her, because she backed up against the door to the room she shared with the other female Indigo and palmed the lock. And it felt good in a sour sort of way to see her afraid, and he shoved her just as the door opened and followed her in.

That was new to her - the whole time he'd been at Battle School she'd never gotten in a physical fight - but that didn't mean she hadn't taken classes (most girls did) and so she fought back. Still, he was bigger and three years older and he ended up pinning her to the deck. To his surprise, she seemed to have fought all the fear out of herself, and she just glared up at him.

He hated her for that, too, and so he let her up and backed towards the door, tonguing a bloody place on his lower lip. She got up faster than he expected, and backed him against the door.

"Better than I thought, McGarvey," she said, and then she kissed him, a hard peck on the lips.

His eyes went wide in surprise - and a little fear? - and then she was backing away. "Get out of my room," she said.

"On my way," he responded, still surprised, too surprised for insults, and opened the door and left. He hated her after that, but sometimes he'd wake up after dreaming about her and wonder what this other feeling that went along with the hatred was.

And sometimes he wondered what would have happened if he'd kissed Jane McIvor back.