海枯石烂我陪你沧海桑田我爱你
[hăi kū shí làn wŏ péi nĭ cāng hăi sāng tián wŏ ài nĭ]
Literally meaning 'Till seas dry up and rocks crumble I'll accompany you; through sea changes I will love you.' It expresses undying commitment to stand beside someone regardless of circumstances or passage of time.