To what degree is Mr. Loisel also to blame for the misery he endures?

In my opinion, Mr. Loisel is only responsible for attempting to make his wife happy. He gets the invitation for his wife.... he could care less about parties. He also buys the dress. None-the-less, it is M. Loisel who advises his wife to borrow some jewels, and after their lost, he should have demanded his wife tell Madame Forestier the truth. Let's face it, M. Loisel's biggest weakness is that he hasn't learned how to put his foot down and say, "We can't afford it."

"How stupid you are!" her husband cried. "Go and see your friend Madame Forestier and ask her to lend you some jewels. You know her well enough for that."