During the press conference for drama 'Fantastic,' The actor said, "If there are two people in the relationship, there must be just one of us left [after the affair]. Either I or my partner must die because I absolutely cannot condone two-timing." That is...a bit extreme but, hey, at least Joo Sang Wook sounds like he will make a faithful partner!
The actor's opinion was a reference to what his character in the drama, Ryu Hae Seong, said to Lee So Hye (played by Kim Hyun Joo). In the series, Ryu Hae Seong had told Lee So Hye that it's okay to cheat in a relationship.
Though it may be okay for a sleazy character like Ryu Hae Seong, Joo Sang Wook put his foot down, saying, "It may be possible for Ryu Hae Seong but not for Joo Sang Wook."