氧气他心脏她
[yăng qì tā xīn zàng tā]
A metaphor suggesting that two people are interconnected on a deep level—perhaps like oxygen ('氧气', vital air for life) to heart ('心脏', core emotional organ). It might imply that their connection is so strong that one person could feel essential to the other's wellbeing just as much as oxygen is needed by the heart.