Pandora

That remembers me of a radio show that aired here a long time ago, the main character (a kid) died in the hospital for a heart attack or something. The people got so mad that the radio station had to change the end of it.

That sounds very sad, especially considering what happened to the actor. And last episodes are sad in general.

Well this is a kdrama called uncontrollably fond, the actor acts like a jerk and hides his disease from the world that way but ends up hurting the girl he loves etc TwT but in reality he can be really sweet. The series ends with him dying while having his head on the girls shoulder. 

the actor got cancer a year after the series ending (where he played someone w cancer)