What is the characterization of Monsieur Loisel in "The Necklace"?

"" is not Monsieur Loisel's story,
so most of what we know about him is conveyed through his connection to his wife
Mathilde.  

M. Loisel is a man who is content with what he has and
appreciates the simple things in life.  In contrast to his wife who is literally never content
(until the end), Loisel is happy with their simple meals.  The first time we meet him,
he

uncovered the soup tureen and declared with a delighted
air, "Ah, the good soup! I don't know anything better than that."

He loves the idea of his wife adorning herself with simple flowers
because she is already beautiful, and we know whatever she is or does is fine with
him.

We also know that M. Loisel wants to please his wife.  Knowing her
desire to be part of the social whirlwind of society, he manages to obtain an invitation to a
formal ball--something that doesnot interest him in the least.  He foregoes his own desire and
savings for a rifle and gives Mathilde the money instead, so she can buy a dress for the ball. 
When she is still discontent, he suggests she borrow some jewelry from a friend, which of course
she does.  At the party, he'd much rather go home early; instead, he manages to stay awake after
allowing her to be as frivolous and flirtatious as she wishes.  Once the necklace has been lost,
there are no complaints or recriminations from him; he simply does what he has to (with whatever
unsavory characters he has to deal with) in order to recover from the loss.

Finally, it's clear that Monsieur Loisel is willing to sacrifice for someone he loves. 
The money he had saved for the gun, as mentioned before, is one example; however, what he does
to pay back the money for the necklace is the definition of "labor of
love."