In the original film, the only scene I remember the two of them sharing is right before Vito gets shot, when Fredo tells him that he will get the car since Paulie had called in sick. However, we see how devoted Fredo is to Vito and how devastated he is by his father's shooting, as Fredo sits on the curb and cries after he fumbles the gun. His love for his father is extremely touching, like a child's devotion. He is literally rendered helpless at the prospect of his father's death.