How horrible must this have been for Chopper to hear from Usopp? All his life, Chopper has searched for his own nakama, someone who will love and accept him for who he is. Right when he finally finds them, one of them tells him that they are no longer family and basically disowns him.
Just like his birth family did.
God, this series stabs you right where it hurts and then just continues to jovially twist the knife deeper.