u/Foxzzzzz_

It's a live-action movie, I think it's a Disney one because I remember seeing it on the Disney Channel.

The protagonist has a brother who accompanies and helps him with his high school problems. Near the end of the film, it is revealed that the brother is dead and is merely a figment of the protagonist's imagination.

The film begins as a normal high school adventure, but the twist changes the entire tone, until in the end the protagonist overcomes his grief and stops imagining his brother.

The viewer doesn't know that the brother is dead until near the end of the film when it is revealed