The story that you are referring to is called "The False Gems," is a story about a man who discovers that his wife must have had a rich lover who gave her fabulous jewels, that he thought were fake. Yes, there is evidence in the story, hints that the gems are real. I did realize that there was a twist to this story. The author drops hints about the real nature of the gems. For example,when Mrs. Lantin says:
Or, once his wife is passed away, and he has to manage his own finances, he does not have enough money to live on, he still doesn't question how his wife had money to even buy fake gems.
"But life soon became a struggle. His income, which, in the hands of his wife, covered all household expenses, was now no longer sufficient for his own immediate wants; and he wondered how she could have managed to buy such excellent wine and the rare delicacies which he could no longer procure with his modest resources." (de Maupassant)
He still does not realize that the gems are real, however, he has no choice once his wife dies, he decides to get rid of them. He tries to sell them and discovers that they were very valuable, only then does he realize that she must have been involved with a lover.