As has been already stated, your "good friend" obviously isn't as good or as much of a friend as you might have previously thought. I suppose the exact circumstances factor in to all of this but when it comes right down to it, I would say since this is a girlfriend and not someone you have committed your life to yet, move on. You should consider forgiving her, but forgiving doesn't mean staying with her. I would say forgive her, but move on. With your so called friend, there really isn't anything to say because this person has proved that they are not your friend. Again, just move on. There are many fish in the sea.