Monsieur and Madame Loisel are entirely different. Their relationship, as many marriages of their time, was meant to be cordial, with the man serving as the primary provider of the household and the woman as the nurturing force of the home. In their case it is not like that. This is primarily because of Madame Loisel.
Monsieur Loisel is a man who is content with his life. He enjoys his broth at nights, and seems to live quite comfortably at the side of his wife. He is a good husband. When the disgrace of the necklace happens, instead of going against his foolish wife, he gives up nearly all that he possesses to be able to purchase a replacement necklace.
Loisel possessed eighteen thousand francs left to him by his father. He intended to borrow the rest.....He did borrow it, getting a thousand from one man, five hundred from another, five louis here, three louis there. He gave notes of hand, entered into ruinous agreements, did business with usurers and the whole tribe of money-lenders.
He tries his best to please his wife, and is "heartbroken" when he sees her upset, which is presumably a lot. He is a simple but loyal, good man.
Madame Loisel is a woman born with a sense of entitlement. She believes that she was made for bigger and better things. This frame of mind is what led her to pick an extravagant looking piece of jewelry from her friend so that she could impress everyone at the ball that her husband wanted so much to take her to. She did impress everyone, as she was a pretty woman. However, her sense of entitlement is such that she really believes that it extends to everything surrounding her, including his servant and her husband, none of whom were appreciated at all by her.
She suffered endlessly, feeling herself born for every delicacy and luxury. She suffered from the poorness of her house, from its mean walls, worn chairs, and ugly curtains. All these things, of which other women of her class would not even have been aware, tormented and insulted her. The sight of the little Breton girl who came to do the work in her little house aroused heart-broken regrets and hopeless dreams in her mind.
Therefore, theirs is a relationship where there is no passion on either part, where one is content and the other is miserable, and where the personalities are so entirely disparate that there is no way to know how they have managed to even stay together.