Min Young had cancer, so TOP go to see her and ask her to leave GD. but, GD misunderstood and thought that TOP actually had affair with that girl.
TOP and the girl were PRETENDING to be together because she didn't want GD to know that SHE was dying from cancer. GD kept getting angry and upset and jealous cause he thinks that TOP just stole his girlfriend.
In the end, while she's in the hospital about to go in for surgery, Taeyang calls up GD to tell him the truth, that SHE has cancer (he decided at the last minute that GD should know, as he trying to give GD a chance to say goodbye)... but he was too late. GD rushes to the hospital, but she ended up dying.
*It's doesn't mean that they didn't want to told GD but, she told them not to tell GD.
dr pena addinfarhani...('',)