Disclaimer: Anything you recognize belongs to JKR.
James looks at you and smiles, and you can't help the wave of guilt that courses through you at his words. "Did you hear what I just said, Padfoot? Lily agreed to marry me. Me!"
And you know that you should feel happy for him, because he is finally marrying the girl of his dreams. But you know better. And you know that despite the ring on her finger and the smile on her lips as she looks at him, at James, that this isn't what she wants. Because James is too blinded – too drunk on love, too high on happiness – to notice anything out of the ordinary, anything out of line.
Because James may have saw her first, he may have loved her first, but that doesn't change the way that you feel. She may have been dating your best friend, but that didn't – couldn't – stop you from falling for her in the first place. She may be engaged to your best friend, but that doesn't stop you from loving her still.
The fact that he is your brother is so many ways was not enough to stop you from that first act of betrayal, to stop your lips from brushing oh so gently against hers in a shadowed corridor. Nor was it enough to stop you from committing that same crime over and over again.
But you both knew it would end this way. You both knew it could never last, just as you both knew that she would eventually say yes to James; it is the inevitable future, written down from the beginning of time. James and Lily – they were always meant to be and you both knew that from the start. And you are just Sirius and James' Lily; lives built on hopes and dreams, and, of course, love, but secrets and lies as well. Neither of you could ever speak the truth, because you could never hurt James that way, and Lily would never hurt you that way.
So as James wraps his arm around her waist and she leans into him ever so slightly, you slip from the room. Because as inevitable as this future was, you've tried – again and again – to fight fate, and watching her go along with it without a word is enough to make you burst, enough to make you self-destruct.
But you know that you can't, and you know that she's right. He is your best friend, your brother, and you would never, could never, hurt him with the truth.
Even if that means you both are living a lie.
A/N: This is my first time writing anything in 2nd person, so let me know if you think it worked okay or was a total failure. ;)