Why does Gatsby tell everything to Nick?

Of all of the people that Jay Gatsby ever associated with, Nick was his only true-friend. Gatsby's wealth was all for an unrequited love that he had for Daisy. Halfway through the novel, he confesses to the lies that he told Nick during their lunch meeting. He wanted to clear the air to show Nick that he wasn't like the other pretentious aristocrats, that his motives, though not pure, were just.