You never realised it wasn't you, you were so sure you were the fire to his ice, the day to his night, Juliet to his Romeo in clichéd of forbidden love. You never realised you were a always a Rose and frost kills pretty, perfect little flowers like you, and, oh, you glittered and shone with the frost on your petals more beautiful than ever but you faded and now your wilted, broken, dead. You never thought you'd be Rosaline. That she with her wild, wild hair a shade darker, with her brown eyes so similar to yours would be his Juliet. You should have, she was always fire. But you thought you could be! You never thought that your perfect, simple beauty of a Rose was nothing compared to the enchanting, flickering beauty of the flames. A Prince needs a Princess and you were always a Queen. So her wild smiles and carefree laughter stole him away and as the Rose wilted they exploded in love and joy. You wanted to hate them. But how could you? They were perfect for each other and you couldn't begrudge your cousin that surely? She was fire to his ice, sunlit day to his dark night, Juliet to his Romeo. Poor little Rosaline. So you were happy for them and you hid from the world.
Well why not? You were Rosaline, the forgotten love, superseded by a glimpse of Juliet, no one would remember, no one would care. People did though. Your mother was furious on your behalf, your father relieved but enraged that anyone dare hurt you, your brother sympathetic, your cousins reassuring and kind, but she was your cousin too and so you hid your feelings, told them you were "fine", "over it", "pleased for them", "relieved" because if this tore your family apart what did you have left? So they relaxed and stopped worrying but they didn't forget you because you might be Rosaline in his story but this is yours and you'll always be the star of the show. So your hid your hurt in the lines of your essays and you buried your broken heart deep within and life went on.
You didn't fool him though, oh, you fooled Romeo and your family followed suit, but not him. You all but grew up together and your acts never fooled him. It took him months of teasing questions and serious conversations but he didn't give up on you and you finally told him that your heart was broken, that you'd thought you were fire not some silly flower, thought the frost wouldn't touch you, thought you'd have that happily ever after, not watch him slip a ring onto your baby cousins finger, that you felt broken and betrayed. He nodded and listened and dried your tears and next time you saw Romeo he had broken nose and you couldn't quite suppress a smile, because while you might not have been fire he knew he was ice and he wasn't blameless for your wilted petals. You hugged him in thanks when you saw him next and he hugged you back hard. You spent more time together than you had for years and he made you laugh and smile, at first you thought he was healing your heart then you realised it felt like it had never broken. He was all too long blond hair, and bright, bright blue eyes and crazy ideas, trouble to your good behaviour, confusion to your planning and you were perfect with each other, and you felt yourself bloom again a Rose coming into flower. Then he told you he loved Juliet and your heart shattered like dropped vase. You ran from the room before he could say another word. You heard him call you name and so you twisted on the spot and was gone. You travelled the world didn't tell anyone where you'd gone, you returned just in time to stop your family self destructing, and so you didn't leave again, but you made sure he never found you, after all, what need did Rosaline have of Paris?
He found you eventually and pressed a letter into your hand just before you apparated away, you couldn't quite burn it but you refused to read it so you put it in the box with all the memories of laughter and sunlight and joy in each other and the world.
You find it a year later while you look for a missing shoe. You see your name and forget who it's from. Before you've finished reading your on your feet and grasping at flu powder. You tumble into his flat crying apologises, for the letter explains his love for you and how insignificant his love for Juliet had been compared to his love for you, all which he had intended to tell you that day years ago.
He turns in surprise at you cries and you fall into his arms, he sees the letter and your expression and your lips crash together, and it's not fire and ice it's sunlight on flowers and somehow it's so so much better. Who says this was ever Romeo and Juliet anyway? Who says it's not Midsummer's Night Dream, after all Lily and Scorpius make a far better Hermia and Lysander than they do Romeo and Juliet. And you were never Rosaline, silly girl, you've always been Helena and Lysander makes a good Demetrius, your all stars in this story and don't you shine.
A Summer later and there's yet another Weasly Wedding, two couples walk down the aisle, one in dusky rose pink and the other in blazing gold. The colours don't quite clash with their hair but they're making a point so they might wear them even if they did. The grooms both blonde wait at the alter, but one is crisp with cool blue eyes, neat hair and icy composure that doesn't quite hid the pure joy burning through him, while the other has too long hair and eyes brighter than ocean with a sunlight corsage and a smile that could light up the sky. You look across at your cousin and smile, she might be fire to Scorpius's ice but your the garden to Lysander's sun and you wouldn't change that for the world.