Why was the guy happy? Or was it just the irony of the whole thing?
O’Henry is all about irony.
He gave her his $1,000 but when he learned that his beloved Miss Hayden stood to gain $50,000 more if he spent his initial $1,000 in a wasteful and foolish way, he grabbed the envelope (showing how he spent his $1,000) and ripped it up, stating that he spent it at the races.