Music is what makes the world go round for Brent Bishop, and the fact that he stops listening to music in the aftermath of the accident in which he accidentally took the life of Lea Zamora shows up how shaken up he was by the experience and how depressed he was. While the fact that he was contemplating suicide before the accident tells us a lot about his state of mind, his sudden lack of interest in music drives home the message of his despair. For Brent, music had always been as important as air or water.
Let us backtrack for a moment, to when is Brent is getting ready to go the party at which all the trouble started. Brent was new in town, and was searching for acceptance among his peers. While psyching himself up for the party, he has the music flowing, even going as far as to use his headphones when moving between the house and the car. For him, music is a way of overcoming unhappiness and anxiety.
Later, Brent pays tribute to Lea by building a harp-shaped whirligig, commemorating the fact that Lea had been a member of an orchestra. In doing this, he realized that a love for music was something that he and Lea had in common.