Guys and girls can't be just friends forever,why?

i think what might happen is when they marry off to other people they may have spouses that dont want them to keep in touch with the other as much and they slowly grow apart..

I think that eventually one or the other ends up wanting more than friendship, which is where things go wrong. I think if you are actually friends and then marry someone else though, it's easier to remain friends because you have something to keep you from feeling that(hopefully). I know that most guy friends I've had before my husband ended up becoming more than friends. But since being with my husband it's easier to just be friends and no more. But the friendships don't last as long. But that could be because I was in the navy though. Friends do tend to come and go in the navy.