你在我左胸第四根肋骨往里
[nĭ zài wŏ zuŏ xiōng dì sì gēn lèi gú wăng lĭ]
The literal translation would be ‘You are inside my fourth left rib’; this expresses deep intimacy as it places someone right next to or within one's heart. It's a poetic way of saying someone occupies the most important place emotionally in your life—your heart lies there.