In Death of a Salesman, what did Willy Loman struggle with, and why may he have chosen to end his life this way?

Willy's inner conflict was, essentially, his fantasy world versus his reality. It is evident in more than just the constant hallucinations that he suffers throughout the play.

Throughout his life, Willy forged a philosophy of life, like many of us do, in order to try to make sense of it. His final product, that is, his idea of life, is that success can be acquired quickly and swiftly if one is well-liked and knows how to work a system. 

To Willy, it was better to neglect the true, inner self in favor of an outer shell that would befit the needs of such system. This, in his opinion, was a formula for success. 

Therefore, Willy bypassed the fact that he was an outdoors man, and that he was great at building things, and decided to enter the world of sales instead of following his true calling in life. He figured that he would make money quickly this way, and become successful.

Moreover, he wanted to lead a life similar to that of a man who did exactly what Willy did: Dave Singleton. A man who supposedly died rich and popular, Singleton became Willy's model of existence, even driving Willy as far as trying to make a name for himself, and leading the life of a high-rolling, playboy businessman.

America is full of beautiful towns and fine, upstanding people. And they know me, boys, they know me up and down New England. The finest people....there’ll be open sesame for all of us, 'cause one thing, boys: I have friends. I can park my car in any street in New England, and the cops protect it like their own.

Sadly, Willy ended up believing that he was really that fake person, while encouraging his children to be the same way: shallow, handsome jocks with clever, smart-mouths, and able to get ahead from the rest the easy way. 

Time, however, starts to affect Willy's over-inflated and false sense of pride. He ages broke, nearly unemployed, never achieving a formal, steady salary at the firm, never really making many friends, and never really having the time or dedication to plant roots from which he could sow any benefit for the future. All he had was his life insurance. 

The hallucinations and constant conflict that he endures throughout the play are signs of the clash between Willy's fantasies and reality; between what was, what was not, and what could have been. All of it pointed out at one thing: Willy will die a dissatisfied, frustrated, incomplete man. His sons will go on living until they meet a similar ending, as well. Something has to give: Willy must sacrifice himself and take himself out of the chaotic equation that is his family, and let them cash his life insurance to start a new life over. This is what Willy's rationale was at the time that he made the decision of ending his life. It was a way to give his sons a chance to have a different destiny.