Haha it's not really cheating. Kim U Jin's father forced him to get married to a "competent" woman. If you watched…
After his mother's death, he had done everything according to his father.. Even his marriage.. And the person he married was constantly opposing his only passion (writing) .. But 1st time in his life someone actually cared about him, prased his writing.. And he eventually fell for her.. Even after that he tried to stop himself for 5 years... Do u really think he's wrong..!! Can u live such a suffocated/unfair life like this!??