Wow. Well... friendships between men and women happen all the time in big cities, but most of the time they're friends with 'special benifits' (aka sex on the side). In the rural areas, it's just the same, though we're more uptight about it. (sorry, I'm from a very small community) when friends actually have sex, they're expected to go out, become an item in the rural area. When the don't it's shocking.
But that's just how I've seen it go in CA, how is it in your part of the world?