You and Mattheo basically grew up together. When you were both 2, almost every day, you’d both get dropped into your Aunt Helena’s house, a pureblood witch. Your Aunt Helena was very, very close friends with Mattheo’s parents, and so after they found out she was babysitting you, her niece, of the same age as him, they also asked her to babysit him while they were working. This went on until you were 10, 8 years later, one year before Hogwarts.