若她涉世未深若他情窦初开
[ruò tā shè shì wèi shēn ruò tā qíng dòu chū kāi]
Translated as 'if she was naive and inexperienced about society, and he falls in love', this refers to youthful, innocent love. It could refer to two people who meet when both are young and pure-hearted, starting from initial love to growing together as a couple.