She is unhappy because she places her self-worth on things rather than the love her husband has for her. She places her self-worth on having things rather than her family and the loyalty her husband has toward her. She was caught up in pretense rather than being simply who she was. In the end, the pretense caught up with her.
In the end, she is ruined because she was enamored of the sparkles and did not realize that her friend had allowed her to borrow only a paste necklace. She was fooled by the sparkles and glitter. If a real diamond necklace had been loaned to her, her friend would probably have shared this information before lending it. As it was, her friend mislead her as well.