相xiāng依yī为wéi命mìng

Literal: leaning on each other to live
Figurative: To depend on each other to get by because there is no one else; the stress falls on having only each other rather than on how they care for each other.

Where does 相依为命 come from?

It comes from the Chen Qing Biao, the memorial Li Mi addressed to Emperor Wu of Jin on being summoned to office. Li Mi had lost his father as a baby, and his mother remarried when he was small, so he was raised by his grandmother. In the text he asks to postpone the appointment to care for her in her old age, explaining that grandmother and grandson, the two of them alone, had each been the other's lifeline (更相为命). The idiom grew out of that line, with 相依 in place of 更相. Today it is used for people who have only each other, very often family, and also for someone living alone with a pet.

Source (出处): 李密《陈情表》

How is 相依为命 used? Two examples

父fù亲qīn去qù世shì以yǐ后hòu，她tā和hé母mǔ亲qīn相xiāng依yī为wéi命mìng，日rì子zi过guò得de很hěn苦kǔ。
After her father died, she and her mother had only each other, and life was very hard.
老lǎo人rén的de孩hái子zi都dōu在zài国guó外wài，他tā和hé一yī条tiáo老lǎo狗gǒu相xiāng依yī为wéi命mìng。
The old man's children all live abroad; he and an old dog have only each other.

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