Their reason

  Shiela couldn't find a man like Dexter, so she is very grateful to him.

"I'm so thankful that I meet someone like you," Shiela smiled as she looked at Dexter.

Shiela's day in the world is numbered as Dexter decided not to waste this opportunity to give Shiela everything she asked for before she passed away. It hurts for Dexter to think that Shiela will also leave his side, but he has to accept it all. Dexter also doesn't regret being able to date Shiela because during their days together, Dexter was also happy and knew that the things he hadn't experienced he had already experienced with Shiela.

Dexter couldn't quite imagine that he would ever find love again with the person who would also leave him. Dexter knows that the person he loves will leave him now, but he knows he has been happy for the rest of his life.