As in the case of wines that improve with age, the oldest friendships ought to be the most delightful.
The trouble is that people seem to expect happiness in life. I can't imagine why; but they do. They are unhappy before they marry, and they imagine to themselves that the reason of their unhappiness will be removed when they are married. When it isn't they blame the other person, which is clearly absurd. I believe that is what generally starts the trouble.