In Sons and Lovers, is materialism what ruins the marriage?

In D.H. Lawrence's novel Sons and Lovers the marriage of Gertrude and Walter Morel began in a whirlwind, and for many wrong reasons. It comes to no surprise that, considering the weak foundations upon which it was built, it crumbled down shortly after it was consummated.

“for three months she was perfectly happy: for six months she was very happy.”

The quote above shows clearly that there was a pattern of decline that set on from the very beginning in the mutual emotions of the couple. We learn that Gertrude, a woman of a humble but well-educated family, is very much a product of her time. Clever and bright, she married miner Walter because of a powerful physical attraction, because this was what was expected of women of her time after being courted, and because Walter was different than her father, who was the only man she could have possibly known.

However, after that first attraction, came the children, the financial problems, and the plenty of unpaid bills that Gertrude discovered seven months after having married her husband. We learn that most of the money has been going to the drink, and that Walter is slowly becoming a rude and violent alcoholic.

When Gertrude discovers that the home where the couple lives is actually part of her property, and not Walter's, Gertrude feels a negative empowerment that is illustrated in the manner with which she starts to treats Walter; she emasculates him and despises him more than ever. This is not materialism necessarily; this is just the only thing that Gertrude can actually call "hers" and she holds on to that idea quite strongly. 

If we conduct a close analysis of Mrs. Morel, we do not necessarily see in her a greedy and materialistic person. We do see a tendency for classicism that comes in and out as a theme throughout the novel.

What we do see in Mrs. Morel, is a woman who is desperate to free herself from her current situation and someone who likes to be in control. She may have thought that she would be happy as a wife and mother, but her choice of husband was clearly not the right one and, what is worse, she does not have the means to at least devote herself to a big and prosperous family. Gertrude is basically suffering the same fate as many women of her time and place: she would very much want to have a chance to change her life and the conditions under which women are subjugated. She knows that this is far from possible.

As a result, she places high stock on the life of her children for two reasons: first, because they are males and second, because Mrs. Morel perceives men as beings who are born free and who have more choices in life. Her strength and influence are evident throughout the novel until she dies of cancer, leaving her son, Paul, devastated. Also, the magnetism and power that she exerts over her kids denotes a woman with tremendous energy and amazing devotion; a woman like Gertrude is, ironically, the force that strengthens her sons' manhood regardless how oedipal they might seem.

In conclusion, materialism is at the heart of Mr. and Mrs. Morel only in terms of what money could provide which, in the case of Mrs. Morel, is control and in the case of Mr. Morel is the temporary relief of alcohol. Materialism in its classical definition is not be the "be all end all" of the marriage as a whole.