Ann compromised but Stew didn't. She was too good for him and it wasn't about the money. In an attempt to prove his "manhood," he trampled all over the common courtesy a husband should have for his wife.
Well, you have to realize this was filmed a LONG time ago - men worked, women took their husband's names and men had pride and were primarily the breadwinner of the family. So, because of all the ribbing he got - he couldn't exactly take it - plus, the coup de grace...being told "YOUR house?" by "Anne" toward the end of the movie.
He knew he would always have to kowtow to her family - face it, no one would like to feel like they were a guest or a second-class citizen while living in someone else's house. How could he ever have self-respect when he'd never be an equal in the rest of the family's eyes...and then, even Anne turned against him in the end...altho she saw she stuck her foot in her mouth - but the deed was done and there was really no winning him back after that.
Yes, we have to look at this through the eyes of people of the 1930's. the audience probably stood up and cheered when Stew told the rich people off, but now it just makes us uncomfortable to see his gang drinking and trashing the house, which wasn't a "mausoleum", as Stew put it, but a beautifully furnished home, that people would like to have today--and the butler would have been mighty glad to have his job.