Happiness Quotient in marriages

How does one define the happiness quotient in one’s marriage ?? The major difference in the Indian and Western lifestyles is the elasticity of relationships, w.r.t marriage. I know everything cannot be quantified, and the topic that I am dealing with is highly qualitative and subjective in nature. Still, being at that stage of my life, I always ponder - how does one define the happiness quotient in a marriage.
I was replying to backfoot’s note on this topic: http://backfoot.rediffiland.com/scripts/xanadu_diary_view.php?postId=1176021318
Now, when one is happily married, why would one seek friendship- whatever friendship it is - either for the intellectual dialogue, or the illicit physical needs. And the fact that one is looking for such companionship, does it in itself an indicator that it is no longer a ‘happy marriage’??
I think that it has more to do with the unedning human ability to be able to love more than one person! (Well, on the humourous side, Gandhi did say, love everyone, equally and I qualify it by saying, love everyone, equally, inspite of your wife/husband)

Too many questions!!

Any thoughts on this one ???