(1) It used to be difficult for the sea to touch the water, forever amber.
It comes from Yuan Zhen's Five Poems of Leaving Thoughts, which means that people who have passed through the sea will see other water, not magnificent water, and after seeing the clouds in Wushan, they feel that the clouds in other places are not worth seeing. The extended meaning is: I only have eyes for you, and only you make me unforgettable.
(2) I wish to have one heart and never leave each other.
It's from Zhuo Wenjun's "The Ballad of the White Head", the original meaning: I thought that if I married a devoted man, I could fall in love and be happy forever. But now people mostly understand that they want to win one's heart and love each other to the end.
(3) It's better to die than to die.
It's from Biography of Yuan Jing 'an in the Northern Qi Dynasty. "A gentleman would rather die than die!" "It is better to be a broken jade than a full tile", that is, it is better to make jade pieces broken than clay tiles preserved. People often use this idiom to mean that they would rather die with noble integrity than humiliation. Sometimes it is also described as being unwilling in love.