Although the character of Monsieur Loisel is not as developed as his wife, we actually do learn quite a bit about him through indirect characterization. He is basically under his wife’s thumb, but he is resourceful. He responds to her every whim, regardless of what he wants. He pays the price for her vanity, but he gets things done.
Monsieur Loisel does seem to be a loving husband. He procures a ticked for a fancy ball for his wife because he thinks she would want to go. He does seem genuinely surprised by his wife’s reaction.
"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. Every one wants to go; it is very select …” (p. 2)
When his wife cries because she does not have enough money to buy a dress, he gives in. He gives her the money he had saved for his gun.
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)
Yet he gives her the money. When she complains further that she has no jewels, he gets frustrated, but he has a suggestion for that too.
"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)
When they go to the ball, it is even clearer that he went for her. He falls asleep while she is still dancing (he is clearly not the jealous type). He swoops in again to save the day when the jewel is lost. He gives her an excuse to write the friend to bide them time, and then borrows the money.
That dreadful debt must be paid. She would pay it. They dismissed their servant; they changed their lodgings; they rented a garret under the roof. (p. 6)
Although she only sees her own suffering, he suffers right there with her. Everything she gives up, he gives up too. He moves when she moves. He takes on extra work. For ten years he labors with her until the debt is paid.
Although the story does seem to focus more on Mathilde, we do learn quite a lot about her husband. He is intelligent, humble, and hard-working. He puts up with quite a lot from his vain wife, and he sticks by her. He will do whatever she wants.