Their perfect relationship was marred forever. No longer could they be completely open with each other as before. They felt the need to cover themselves. Hiding from God, hiding from each other. That's the natural way that unregenerate, unconverted human beings act.
Fear is the core emotion in our human personality.
And the source of our fear is an awareness of our profoundly unnacceptable condition. We hide from each other. We put on defensive layers. Masks if you like. And Satan stands there happily handing them to us to try on.