白头偕老

1. • (of a married couple) to live together until old age to remain lifelong companions

     idiom

Character by character

• 白(bái)surname Bai
• 头(tóu)head
• 偕(xié)in company with
• 老(lǎo)prefix used before the surname of a person or a numeral indicating the order of birth of the children in a family or to indicate affection or familiarity