The story that you refer to is "The False Gems," in which the main character M. Lantin is married to a woman that he truly loves, he adores her, as the years pass in their marriage he loves her more and more. There are only two things that he does not like about her. She loves to attend the theater and has a passion for fake jewels.
The irony of the story, situational irony, where an outcome is completely different that what is expected is evidenced in the "false gems." Also, verbal irony, M. Lantin's wife knows that the gems are real, but she pretends that they are fake.
After his wife dies, his life is miserable. He can't stand the sight of the gems that his wife brought home constantly. By now he is poor, destitute. So he decides to sell the gems.
The irony is that when he tries to sell them, he learns that the gems, the jewelry is in fact real and very valuable. M. Lantin sells the gems for a great sum, now he is wealthy.
His wife must have had an admirer, a rich one, who gave her the gems as gifts. So in fact, his loving, attentive wife, was probably having an affair. Yet he never knew it, he was shocked.
M. Lantin decides to remarry, his second wife is very virtuous, she will be a faithful wife.
The irony is twofold, M. Lantin never knew that the gems were real and that his first wife was technically, false.
The second wife, who should make him happy with her fidelity, makes him miserable.