Luhan has been cheating behind Sehun. 

Sehun loved Luhan, making Luhan as the reason he lived.

But lately, Luhan have been ignoring Sehun.

Though Luhan doesnt really noticed of his own actions.

But Sehun did.

He knew this would happen eventually. That time when Luhan would surely leave Sehun for another man.

and Luhan regretted it.