Sehun's too desperate to get his hands on those expensives medicines which have been prescribed for his mother that he's willing to do absolutely anything. He's sold anything they didn't really need, to save up some and now that he knows the exact amount of money he should pay, all the thoughts of finding a healthy, normal job leave his mind. So instead of continuing his job as a bartender he agrees to give his ity to someone he has never met and signs all the contracts given to him without even glancing at the words written on those papers. 

He thought he would fall in love someday

But he lost everything so suddenly that's he's ready to do anything

To save the only family he has left

He'll give up on love and maybe even friendships

All he really needs is his mother to live a happy life

Even if it means that none of his wishes would come true

Little did he know that there will be people in his life

Who are willing to do the same thing

To make sure Sehun lives a happy life and not them

http://www.asianfanfics.com/story/view/935746/the-beginning-of-lust-abuse-angst-exo-sekai-kaihun-sebaek-ionau