Everyone assumes they know Mattheo Riddle. The flirt. The troublemaker. The Dark Lord's son. The boy who moves through people effortlessly, leaves before things become complicated, and treats attachment like something to be avoided at all costs. Y/ N knows him too. Or at least she should. Raised within the same elite pureblood circle, they've spent their entire lives in the same rooms. The same galas. The same Ministry functions. The same holidays. The same friend group. Draco. Theo. Blaise. Lorenzo. Pansy. Mattheo. You. Always together. Yet somehow never close. Not really. The strange thing is that despite the distance between mattheo and Y/N, they know each other better than most people ever could. She knows exactly when Mattheo is putting on an act and when he's genuinely amused. She knows what mood he's in before he speaks. She knows which jokes are real and which ones are designed to keep people away. Mattheo knows her routines, her habits, the books she rereads, the expressions she makes when she's annoyed, and every version of her smile. They know everything. Except each other. Then sixth year changes everything. One impulsive night turns into another. And another. Until they find themselves trapped inside an arrangement neither of them planned and neither of them wants to end. No labels. No expectations. No promises. Just two people finding comfort in each other in the quiet hours between parties, family obligations, and the expectations constantly hanging over their heads. It should be simple. Mattheo doesn't do relationships. Y/ N doesn't do messy. And neither of them are willing to risk the friend group they've spent their entire lives building. But the arrangement begins creating problems neither of them expected. Mattheo becomes possessive without meaning to. Y/ N starts noticing things she never paid attention to before. Jealousy appears where it shouldn't. Boundaries blur. And suddenly the person