It's an age old question that's not been answered, and if it has been answered women seem to have a different view on the matter than men. I find it almost comical that all the men surveyed in this video didn't think that men and women could be just friends. The implication being that men are attracted to women and naturally want to get out the friend zone at some point.
Maybe it's human nature, but there is a real tension in relationships surrounding you partner having friends of the opposite sex. You may not want to admit