Death of a Salesman

Throughout the entire play Biff and Willy don't get along. In my opinion it seems as though all Willy wants is the connection that he and Biff had before Biff found Willy having an affair. After this key moment in the play, Biff and Willy no longer have the loving father son relationship that they once had. In the end of the novel Biff and Willy finally make up. It is right after this that Willy gets in his car and kills himself. Why did he want to kill himself when he and his son finally made up?