Well, temptation period. One has to be careful when they're married and commited because the underlying man/woman attraction and question will always be there. No matter what. People try to think that they can "just be friends" without any biological attraction being there, and it may not be, or to a dangerous degree at first, but it grows.
And people who say, well this is my friend of the opposite sex, and we've known each other most of our lives, so you have to accept this...No you don't. You're married now and that is a dangerous situation.
Not that it isn't possible to be platonic friends...but it isn't likely in most cases. And if the married couple can not comprehend this and show reverence and respect for the marriage...then it's likely they're lying anyway! :yes