Basically, Seo-in's brother Jaewon used to bully Yeongwoon badly. To protect her son, Jaewon's mother paid hush money to Yeongwoon's father so that the issue wouldn't get widespread. Seo-in's mother knows that Yeongwoon was bullied by her son. This is given as a reason why Yeongwoon and Seo-in grew apart and why he seems to have panic attacks.
Hae-yool, the guy Yeongwoon used to be the manager of, wanted to use this article to blackmail Yeongwoon because he knows that any potential fall-out of this case going public would also affect Seo-in. He knows Yeongwoon would want to protect Seo-in from that and so he gives the article to Yeongwoon.
Taegu, the loan shark guy in an effort to keep Yeongwoon and Seo-in apart, also sends the article to Seo-in so that he's aware of what the family has done to Yeongwoon and why they grew apart. Seo-in doesn't understand that Yeongwoon is the victim here and thinks that it is one of the many victims of his bully brother Jaewon and doesn't care.
Things come to a head in the last few chapters when Hae-yool reveals to Seo-in that the victim of the bullying case was infact Yeongwoon himself. There are also pictures which indicate how badly he was bullied by Jaewon.
Basically, Seo-in's brother Jaewon used to bully Yeongwoon badly. To protect her son, Jaewon's mother paid hush money to Yeongwoon's father so that the issue wouldn't get widespread. Seo-in's mother knows that Yeongwoon was bullied by her son. This is given as a reason why Yeongwoon and Seo-in grew apart and why he seems to have panic attacks.
Hae-yool, the guy Yeongwoon used to be the manager of, wanted to use this article to blackmail Yeongwoon because he knows that any potential fall-out of this case going public would also affect Seo-in. He knows Yeongwoon would want to protect Seo-in from that and so he gives the article to Yeongwoon.
Taegu, the loan shark guy in an effort to keep Yeongwoon and Seo-in apart, also sends the article to Seo-in so that he's aware of what the family has done to Yeongwoon and why they grew apart. Seo-in doesn't understand that Yeongwoon is the victim here and thinks that it is one of the many victims of his bully brother Jaewon and doesn't care.
Things come to a head in the last few chapters when Hae-yool reveals to Seo-in that the victim of the bullying case was infact Yeongwoon himself. There are also pictures which indicate how badly he was bullied by Jaewon.
Correct me if I'm wrong though.