Author's Note: Dedicated to sunnysmile (my first signed review giant grin) who pointed out that Lily came off as being a bit selfish – after reading all the chapters again I saw your point; so I turned it into a drabble. :D
Patterns of Behaviour
James knew that she didn't do it because of any conscious belief that she was more important than him in their relationship. By this point it was a habit ingrained into her by the years they spent perfecting their shtick. Before they started dating, they had reached a point when each of their encounters conformed to the same innate algorithm.
Step one; James displays his affection for her in some garishly public, exuberant way that reinforces her unfair but understandable (based on past behaviour) belief that first of all, he does this partly for attention and second of all his feelings are shallow and therefore the chase is probably what appeals most to him.
Step two; following said public demonstration, he asks her out for the n-hundredth time.
Step three; Miss Evans rejects him for the n-hundredth time with a witty, cutting remark, missing the way the twinkle in his eyes dims, and in the prefect years exacerbating the wound by giving him detention or taking points off Gryffindor.
Lily was the type of person who was cruel without intent or malice; in darker moments, James couldn't decide whether this was better or worse than people who were deliberately cruel. Her tendency at times to be oblivious to his feelings was the character flaw (in her) which caused the most damage in their relationship. The flaw on his part which accompanied hers was his habit of silence. Lily rarely knew when she had hurt him because he rarely let it show that he had been hurt.
This morning Sirius had visited; if he hadn't Lily would probably have never been enlightened about how much it bothered him when someone was careless with his chess set. The set had been a gift from a great uncle James had been very close to from childhood up to the age of thirteen when he had passed away. Lily thought wizards chess was a barbaric game (though she always played when he asked) and she tended to pick up pieces and just dump them in the case after a game, missing the way he winced.
As she had started her dumping ritual, Sirius who had been watching had said "That right there is proof of how much Prongs adores you. No one else gets away with handling that chess set the way you are right now." Lily had seized on the comment and made Padfoot explain everything. Afterwards she'd been so remorseful (and near tearful) that James had felt guilty.
Those were their flaws; James would work on talking to Lily more, and Lily would try harder to listen. James had been hurt too many times whilst chasing Lily Evans, he refused to let their bad habits ruin these years when he finally had her.
