你是我左边的心跳你是我呼吸的空气
[nĭ shì wŏ zuŏ biān de xīn tiào nĭ shì wŏ hū xī de kōng qì]
This nickname expresses deep affection for someone. It metaphorically describes that person as vital and indispensable, indicating the user is deeply in love or dependent on this person as much as they depend on their heartbeat and air to live.