Monsieur Loisel is not described as vividly as his wife Mathilde. In fact, he is not even given a name! Most of the characterization of him is indirect. You can describe him as loving, frustrated, satisfied, clueless, and honest.
Monsieur Loisel is a loving, if not subservient, husband. He wants to do what his wife wants, or anything to make her happy. He sacrifices his comfort for hers.
He grew a little pale, because he was laying aside just that amount to buy a gun and treat himself to a little shooting next summer on the plain of Nanterre…. (p. 3)
When she asks for money for a dress to go to the ball, he acquiesces and gives her the money he has set aside for himself.
Mathilde’s husband is also frustrated though. He knows he cannot give her everything she wants. This bothers him. Yet he also gets irritated when she is constantly asking for more.
"How stupid you are!" her husband cried. "Go look up your friend, Madame Forestier, and ask her to lend you some jewels. You're intimate enough with her to do that." (p. 3)
Although this seems mean, it must not have been mean in the way he said it. She does not get upset. Instead, she is thrilled. She “uttered a cry of joy” and took the suggestion.
Monsieur Loisel is satisfied. Although he is only a clerk, he does not seem to mind his life. He suggests that Mathilde put flowers in her hair instead of wearing jewels, because it is fashionable. He does not understand why she does not want to go to the ball. He is satisfied with his life, and is not sure why she is not.
Mathilde’s husband does not seem to understand how unhappy she is. He is fine with his life.
"Why, my dear, I thought you would be glad. You never go out, and this is such a fine opportunity. I had great trouble to get it….” (p. 2)
He did not understand that she would be upset when he got her the invitation because she did not have the right clothes. He is clueless, and could have avoided a lot of trouble by not opening that can of worms.
Finally, Loisel is relatively honest. When the jewel goes missing, he has it replaced. He does lie at first.
"You must write to your friend," said he, "that you have broken the clasp of her necklace and that you are having it mended. That will give us time to turn round." (p. 5)
However, he is just biding his time. He does work very hard to replace the jewel.