Hyeon Dae and Min Joo thought one of them getting married would end the sex-partner relationship. However, they can't hold in their desires and Hyeon Dae destroys himself with sex, while Min Joo can't give up what she can't have.
Healing Mate
The Invited Man
Game of Thrones - Conquest & Rebellion: An Animated History of the Seven Kingdoms
Newlywed Hell