In Kingdom Hearts, there are so many people who are regreting what they chose. In this song, it basically has the singer asking if he's supposed to be happy.
WARNING: WATCH VIDEO BEFORE READING ON.
Alright, the point of views switch like this: After the songs introduction (which is after my big intro) and a small, sad looking clip of Roxas, there is Sora fighting against Riku to save Kairi. That is Sora's point of view. Then it switches to Kairi when she wakes up. The next scene with the tree and the three friends is basically Riku's point of view, because the song talks about stories, and in the long version of that scene he does kind of tell and story..? So that and the part where he accepts the darkness are his point of view. Back to Sora and Kairi, this little scene is mostly Kairi's point of view. But it is kind of shared between those two.. Next, Roxas. Of course, this is his point of view. Don't really listen to the words of the song, but to the words on the clip.