EDIT BY LANCE - the following synopsis gives names from the Chinese version of this series.

Chinese Synopsis
Lu- zhu a 23 yrs girl, suffers from insomnia, Lu-zhu met her student Xu Juiang-xu, a troublemaker, while she teaches in a middle school, Lu-xu falls in love with Xu Jiang-xu, her 19 years old student. They support and love eachother. their love wins their friends and relatives understanding. however, lu-zhu has got an kim-tai-xian, her engaged boyfriend. lu-zhu fall in love with Jiang-xu despite all this. Unfortunatley, Jiang-xu was put in prision because of accidental murder.
5yrs later, lu-zhu and jiang-xu meet again, but lu-zhu has been engaged with another man. and jiang-xu also has a new girlfriend ,ji-jin, his ex-schoolmate. the love of these four young couples begins to changed. their love is so passionate and mind-blowing.

Korean Synopsis
It's a love story between the disobedient student Kang-wook and his teacher Yool-ju set in a high school in Chuncheon.

Before meeting Kang-wook, Yool-ju has been dating Tae-hyeon, a public prosecutor. But over time Yool-ju and Kang-wook fall deeply in love with each other despite social prejudices, the age gap and the teacher-student relation. One day, Yool-ju accidentally kills Kang-wook's classmate who intentionally harasses Kang-wook. But due to narcolepsy, Yool-ju doesn't remember what has happened, as she falls asleep during the incident. To protect her, Kang-wook goes to jail in place of Yool-ju.

Five years later, when Kang-wook is released from prison, he meets with Yool-ju again, but Yool-ju is engaged to Tae-hyeon. Learning what sacrifice he has made for her, Yool-ju wants to return to Kang-wook, but this time Kang-wook is not alone -- Ja-kyung, his former classmate and currently a radio program host, is beside him. The circumstances hamper Yool-ju from loving Kang-wook, but she is desperate to help him recover the lost five years and become a top-notch cook.

I THINK I GOT 2 WATCH THIS
I HAVENT WATCH IT TILL NOW