Haven't read all this properly - just a quick skim.
I can see why our society has evolved the way it has, why marriage is, in our current cultural setup, a good thing, and why adultery is therefore a bad thing.
But is our current cultural setup right for us at all? I would suggest not - depression rates are the highest they've ever been - even those who are not officially depressed are usually living a fairly see-saw existence - down in the dumps fairly frequently. It seems we all accept that this is simply part of human nature.
A brilliant book called the 'Continuum Concept' (that spelling may be completely wrong) talks about life in a tribe, where the humans are carefree and happy - all the time - its their natural state. The author mainly focusses on child rearing methods (her point is that the methods used make the people happier). I don't entirely agree with her here, but the basic gist I get out of it is...
Women spend time together in groups doing activities such as gardening/farming type stuff, cooking, feeding babies.
Men spend time in groups hunting. Children spend all their time together - the older ones looking after the younger ones, and the younger ones only turning to their mother or alternative woman in the group when they have a strong need for her.
Everyone happy. All roles clearly delineated. Everyone has their own role, their own 'busy' activity - less time for introspection/self analysis. Noone arguing over whose turn it is to cook/wash up/do the diy. A shared culture passing on child rearing skills - the older girls learn from watching their mothers and the other women in the group. Women aren't left to 'entertain' their children on their own all day every day.
So what does this have to do with marriage? Well I think the main problem with our society is the whole darn set up - men and women just aren't built to live together in twosomes, and children aren't built to live with just their parents for company and stimulation. Men, women, and children all function much better when spending time with their own group.
Which is why, in our society, men and women make each other so miserable, and why men are happiest out with each other down the pub, women are happiest chatting to each other, and children are at their best left to play with other children.
Of course there is no way we will ever attain this level of nirvana in our messed up society now. But, hey, at least we have great healthcare and don't die of random diseases like happy folk in tribes do.