Trust
Rose Weasley doesn't trust many people.
No, that's a lie. She trusts her family, and there are a lot of them. But outside of blood relations, her close friends are few and far between. There's Albus' girlfriend, Jennifer, and the Scamander twins, though they are more like family, and a select few housemates, like Alice Longbottom, who she has grown close to over the years.
But in her 17 short years, she has trusted very few as much as she trusts Scorpius Malfoy. This, she muses, is ironic, considering the centuries of bad blood between their families.
But life is funny that way.