One and Only S01E03 - Seems like Cui Shi Yi has feelings a little more than a teacher for Zhou Sheng Chen.

Zhou Sheng Chen needed to head for another war which may take several months. On the other hand, the Crown Prince is looking forward to their engagement which was bound to happen in the future. Before when they went on a war, his entire mansion used to be empty, but this time there is Shi Yi staying there. Zhou Sheng Chen tells Shi Yi about him heading for another war. After several months there is still no news about him. Staying at his mansion, Shi Yi finally is able to talk a little bit. She finally hears from him and visits him at his Military Camp.