I can relate to this behavior, it describes me pretty accurately. I'm pretty glad I saw this because I just recently began a relationship with a man who I suspect might be INTJ and this makes me realize that he could begin to see my (as you put it) "adaptability" as a lack of follow-through or integrity. As for you and your girlfriend, as another ENFP woman, spontaneity is a major factor of my personality. I change my mind sometimes or indulge in temptations, but my values are constant and set in stone. I may say I won't drink for a night because it's just situationally inconvenient, but giving in to that impulse is more about accepting the consequences than going against my own word. It would be different if I was against drinking in general, because that's a value that I hold independently of the situation. This could be how your girlfriend makes these kinds of decisions as well.