I dont think its a good idea. When you are friends, there are still somethings they dont share; well they cant see it then after all they are best friends. But being married is all about 24*7 together.. every angle every emotion, may be they start seeing two different people suddenly and end up in bad taste. Let friendship be friendship, well I can say the other way round is ok, if your wife is your best friend, then you will be a good human being and the family wil be happy forever.
