Movie

But of course, the exchange with the devil eventually leads to death as soon as the deal between the devil and the contractor was finished. The devil will collect the contractor's payment as soon as the devil fulfilled his end.

In that movie, the devil ended his deal with the protagonist. But, because he has fallen in love with the protagonist, instead of taking away the soul of the protagonist, he didn't do it as per their contract stated. Thus, he received a backlash when he refused to take away the protagonist's soul. As for the protagonist, he has actually fallen in love with the devil, too. The devil's arrival is like the light in his life – even if the devil was supposed to be on the dark side. So, when their contract finally ended, the protagonist wholeheartedly gave his soul to the devil.