How does Ben affect Willy? How does he influence the events in the play?

Ben is the person Willy holds up as an example of success. He calls his brother a genius, and he looks to him for advice. In fact, it's after the imaginary conversation he holds with his brother that finalizes his decision to commit suicide.

Ben affects Willy because he represents everything Willy is not. Ben was wealthy and offered Willy opportunities to enjoy some of that wealthy by working with him. However, Willy declined; now Ben has died and Willy only seems him in retrospect or in conversations that he imagines.