Disclaimer: I don't own any Harry Potter, though I wish I did.
Realizations
When James Potter first meets Lily Evans, the only reason she stands out in his eyes is because of her shockingly red head of hair. It's because her hair is so garishly bright and he's just never met anyone with that shade of red hair before that he remembers her.
As a first year, James knows Lily as the smart girl in his class who always answers questions correctly. She seems as if she'd be an interesting person to talk to, and Remus certainly thinks so, as the two have become good friends already. But James must agree with Sirius. There are so many more fun things to do, so much mayhem and destruction they can be wreaking, who can really be bothered to talk to a girl?
As a second year, James doesn't pay much attention to Lily, except in passing. He is, after all, part of the Quidditch team now, and has much more important things to do. He is kept busy with his late-night escapades with the newly formed Marauders after receiving an invisibility cloak from his father over the summer.
As a third year, James notices that Lily is really quite fun to make fun of. She responds so wonderfully to jibes and taunts, possibly due to that infamous wicked red-haired temper. Sirius teases James, saying that James must like her because why else would anyone expend so much thought and energy over someone else. James tells Sirius to quit being a stupid prat and to stop bloody joking around because it isn't funny.
As a fourth year, James continues to pick fights with Lily because he discovers that he really does enjoy doing so. Lily begins going out with a fifth year Ravenclaw named Philip. Within a month, James, with the help of the Marauders, successfully breaks up that budding relationship. James tells himself that he was doing what's-his-name a favor. After all, a nice, quiet bloke like him deserves a nice, quiet girlfriend, not the spitfire of a girl he knows Lily to be.
As a fifth year, James finds that he can't stop staring at Lily. When did she become so pretty, he wonders. The hair that he used to think was so disgustingly bright is still the same color red, but somehow it seems to suit her perfectly now. As luminous green eyes sparkle and she laughs at a joke, James is disgruntled to find that he is not the only one staring.
As a sixth year, James decides that Lily is perfect and wants to date her. To him, she is the most beautiful, intelligent, and confident girl in school. She is second to none, and he wants to claim this perfection for himself.
As a seventh year, James realizes that Lily isn't perfect. He finds that he doesn't mind, though. In fact, he actually likes her more because of that. He thinks it's cute, the way she chews on the end of her quill when deep in thought although it really can't be sanitary and the way she trips over her feet sometimes.
He loves the way she gets angry at him, cheeks red, eyes sparking, and spitting fire. Lily is magnificent in her rage. Irksome as it may be sometimes, he also admires her stubbornness; how she can stand up for what she thinks and never back down, not even to him, especially not to him. He even loves the way she gets on his case sometimes because it shows that she really does care about him.
He also loves the Lily who is unsure of herself, who is hesitant and uncertain. When James sees such a heartbreakingly vulnerable Lily, his chest aches and he suddenly finds it hard to breathe. He wants to take her in his arms and shield her from everything, even if only for a moment, because although he knows she is strong enough to face the world on her own, he just wants to show her that he is there if ever she needed a shoulder to lean on.
When James finally convinces Lily to give him a chance, he can't stop smiling for a week. At the end of their first date, they linger at the foot of the stairs to the girl's dormitories, neither unwilling to leave quite just yet. After a few minutes of quiet conversation, James tentatively leans in for a goodnight kiss and as their lips meet, his head feels light, his stomach feels fluttery, and his heart feels so full it might burst, and he would like to stand here and say goodnight to her over and over again for the rest of his life.
It is at this moment, when he can't tell up from down and the room is spinning dizzily around him and all he can concentrate on is this girl in front of him that he realizes that Lily is the girl he will marry one day.
