Once We Get Married Episode 21

Upset Xi Xi is fine to be away from him for 3 months while studying, Si Chen decides to secretly spy on her. He’s able to insert himself as a guest lecturer at her school, but keeps his true identity anonymous, taking on a new identity as Mr. Zorro. He is eventually found out by Zi Xin and Xi Xi, but eventually gives Xi Xi the freedom and space to follow her pursuits. (Source: frankly at kisskh)