沧海桑田青梅竹马
[cāng hăi sāng tián qīng méi zhú mă]
Translates roughly into 'Childhood lovers through all changes.' The phrase “沧海桑田” (cānghǎi sāngtián) means 'great changes have occurred over time' while “青梅竹马” describes two people who grow up together from a very young age. It's about a long-standing, deep relationship.