Yeh Rishta Kya Kehlata Hai: Kartik LIES to family about his marriage with Seerat

In the serial Yeh Rishta Kya Kehlata Hai, Kartik has lied to his family. He tells his family that Seerat and he are married now. On the other hand, Seerat questions Kartik about his statement. But why did Kartik take such decision? Will the family be able to find out the truth? What will happen when Kartik's lie is exposed?