Mathilde thinks they don't have any money and she wants more. She thinks that she deserves a rich husband, while her husband isn't rich but he provides.
Climax
I LOST THE NECKLACE
Mathilde loves jewelry, clothes, shoes, etc. But she doesn't get everything she wants because she isn't rich. She wants to be and she doesn't even love her husband.
Falling Action
Can we borrow money?
Her husband got invited to a rich people's party and wanted to bring his wife, but Mathilde started crying because she doesn't have anything nice to wear so he gives her money. She also borrows a necklace from a friend.
Resolution
I lost the necklace.
It was fake!
They were at the party till 4 am but she realized that she had lost the necklace so the husband went to look for it.
Since she didn't want to tell her friend that they had lost the necklace they asked a bunch of people to borrow their money and she will pay them back. She worked off her debt for 10 years and realized that she is now poor...
After years of working off her dept, she told her friend that she had lost the necklace and bought a different one to give her only for her to find out it was a fake necklace that her friend gave her. She worked all that time for no reason.