Why do some important friendships become dispensable?

Ever wondered how some relationships that you hold so close to your heart suddenly seem completely irrelevant, how you just can't relate to someone who was once your soul sister, how there's a complete disconnect with friends who you once shared an almost telepathic connection with?

My colleague was just telling me the other day, how she can no longer have a normal conversation with her childhood friend anymore. Every time she tried having a coherent conversation, all her friend could talk about was the latest trick her three-year-old was up to.  She had so much to tell that she had no time to listen to my colleague. You might say, "Oh c'mmon, there's nothing wrong with being an indulgent mother." No, there's nothing wrong with being indulgent about the apple of your eyes but are we so busy obsessing about our little wonders that we have no time to listen to a friend who probably just needs a patient ear?

My cousin had a friend who was so indispensable that after a point he too became family. He would be there for birthdays, weddings, festivals, deaths, hospital visits, late night parties ... okay, you get the drift. Even after my cousin got married a few years back, his friend continued to be a part of the extended family. I met my cousin last month and for the first time in years there was just no mention of the omnipresent friend. I wondered what had gone wrong and on further prodding heard that the "friend" was now a married and changed person. I guess, that says it all, some people after signing on the dotted line manage to mutate into a being you just can't identify with anymore.

My best friend, my drinking mate, my dancing buddy, my non-judgmental soul-mate has suddenly transformed into this burkha-clad smug-married woman who can't stop gushing about her husband and how wonderful he is. I understand her excitement about the new change of status but what happened to the fun person I knew a few weeks back? Instead I have this health-conscious teetotaler who is forever talking about the ill-effects of smoking and drinking, especially among women.

Don't get me wrong, I am neither underplaying the excitement of marriage/motherhood/parenthood nor am I advocating alcohol use, all I am saying is do these roles demand such dramatic change of personality, that you become unrecognizable to friends who once knew you the best? And, indeed if it does, then you sure can't expect to keep your friends to be as accepting of you in your new avatar.