待你长发及腰我要做你伴娘
[dài nĭ zhăng fā jí yāo wŏ yào zuò nĭ bàn niáng]
This translates to a romantic notion: 'When you grow your hair long enough to reach your waist, I want to be your bridesmaid'. It signifies unwavering loyalty and desire for being closely involved in someone’s life, specifically when significant milestones are achieved like getting married.