These words are spoken in a conversation between the story's protagonist, Charles Wales, and a bartender. Charles, who's rapidly turning into a full-blown alcoholic, is drowning his sorrows in a bar. Charles is feeling pretty depressed, and it's no wonder why: just about everything has gone wrong with his life. First of all, his wife, Helen, died in a tragic accident. Then, his daughter, Honoria, was taken from him and placed in the custody of Helen's puritanical aunt and uncle. If that weren't enough, Charles proceeded to lose most of his money in the Wall Street Crash. All in all, then, Charles's life has been circling the drain these last few years.
As the bartender serves Charles yet another drink, he can see the look of depression etched all over his face. It's then that he asks Charles if he's depressed because of all the money he lost in the stock market crash. Charles replies as follows:
I did, but I lost everything I wanted in the boom.
What Charles means by this is that he lost what was most important to him—his daughter, Honoria—during the economic boom that preceded the Wall Street Crash. Yes, he's depressed because he lost most of his money when the stock market went south, but he was already depressed before then because the thing that mattered most to him in all the world, his daughter, was taken away from him.