What's the secret to long-lasting relationships?

I chanced upon two very different articles on the theme of modern day relationships. Both are incidentally in the Guardian. 

The first is "Infidelity: oh, stop fretting. It's only an affair." 

This one talks about an upcoming book by Catherine Hakim, The New Rules of Marriage. Apparently, British society is too strait-laced when it comes to infidelity and if it accepted affairs more often, marriages would last longer. Interesting argument. 

I never knew that British society was so strait-laced in comparison to the Mediterranean ones where apparently affairs are treated with laissez-faire and flexible attitudes! I usually lump Western society together. I know off hand that American society is probably more conservative than so-called old-world Europe but where divorce rates are quite high. I seem to read different articles that Europe has in fact replaced marriage and that people are rejecting this institution for its legal and moral self-righteousness. At the same time, one also reads articles about a return to religious values, marriages and so-called family values. Which is true?

I suppose there are multiple trends happening at the same time. One could say something as cliche as modern and traditional forces are always in tension. 

I wonder whether the question to ask here is whether or not we should be more flexible with marriages but how relevant the institution of marriage still is. Why get married? How important is it to have the big wedding? What does a marriage mean, in the end? A piece of paper? And, how can we differentiate these questions for women and men?

The second article is a commentary on the political-economy of modern relationships and social status with regards to capitalism: "

Ewan Morrison: what I'm thinking about ... why capitalism wants us to stay single."

It is completely opposite to the analysis in the first article. 

I think the introduction of this article says it all: "We like to think we're free in the free market; that we're beyond the forces of advertising and social manipulation by market forces. But there is a new social trend - the rise of 'the single person' as model consumer - that presents us with a paradox. What we once thought of as radical - staying single - may now be reactionary."

I found this statistic very interesting: "Singles consume 38% more produce, 42% more packaging, 55% more electricity and 61% more gas per capita than four-person households, according to a study by Jianguo Liu of Michigan State University. "

According to the article, capitalism has been cashing in on social changes. Apparently, "Being single, has since the 60s been seen as a radical choice, a form of rebellion against bourgeois capitalist conformism."  Capitalism has caught up and is now focusing on the single consumer. 

I'm not sure whether I entirely agree with that. There's a huge wedding industry in Europe and the US. People still spend a lot of money on getting hitched and showing it off to the whole world. There is still a lot of pressure on people to copulate and make it legal. There is also a huge divorce industry that cashes in on people separating and their assets. 

What do you think? How much farther do you think we will stretch our notions of relationships, marriages or even friendships? Is it a matter of learning, un-learning and teaching ourselves what suits us best? Are our notions outdated and do we need to constantly evolve? And how much of a role do market forces play in social status?