There is something between them, but she doesn't want to admit it.
Their relationship is convoluted in a way she is only half aware of. They will never be friends, perhaps. She thought they could be; she wanted them to be. But there is too much between them, too much history, too many arguments, too many hurt feelings, for them to settle down into anything vaguely resembling a friendship.
(Too much passion.)
He riles her. She likes to consider herself an even-tempered person, easy-going, easy to get along with, even if she does say so herself. No one can get under her skin like he does. And yet under all that, there's something about him...
She needs his attention. This much is undeniable. It has got to the point where it doesn't matter to her if they are exchanging pleasantries, or disagreeing, or full-on arguing, or on cool-but-civil speaking terms after insults have been swapped. And yet despite this, she has always enjoyed their arguments. And this is where the convolution begins.
("Yell at me if you want, Evans. But don't try to tell me you want me out of your sight. That's not fair on either of us.")
She suspects he knows what he does to her. That being with him – doesn't make her happy, exactly, not all the time anyway. Not when they're arguing, or he's being condescending, or she's said something to hurt him and the guilt is eating her up inside. But it's something like a drug to her now. She can't help but be aware of it, and it's at times like that when she feels like she's on the brink of something momentous; one move and she could either have him or lose him forever.
And he knows what he does to her.
It is for this reason that she believes he winds her up on purpose. He knows that while she likes the fact that they can act like friends, she likes better the disagreements between them that prove how much she cares. Without the fighting, there would be apathy, and with apathy would come the end. And even though he pretends to be offended when they fight, she sees the delighted grin at the end of the dispute that shows her that he wants it just as much as she does.
("That charm that everyone else gets, Evans, where does it go when you're talking to me?")
Oh, and she can try to convince herself that she doesn't want to feel like this. In fact, she tells herself this on a regular basis. Every unkind word, every irritated exchange, and she audibly bemoans the fact that she ever was inconvenienced by James Potter's existence. But she's lying to herself, and she knows it. And more to the point, so does he.
"Hey, Lily."
Two words are all it takes, and she falls back into the same familiar pattern that they've been a part of for as long as she can remember.
She needs him. This much is undeniable.