"Diamonds Are For Heather", the first depiction of Del's pining for a family. After taking to a young mother (whose husband had abandoned her) and growing attached to her son, he proposes to her, only to be turned down, her husband having returned asking for a second chance. It would be a long while before Del finally got to be a family man.
The scene where Rodney breaks down in the elevator after Cassandra's miscarriage in "Time On Our Hands".
In "Little Problems", where Del is left alone after Rodney goes off to his honeymoon and new life.
The funeral for Grandad in "Strained Relations", and the part afterwards where Del puts his hand on Grandad's chair, now empty.
Rodney describing his feeling "cheated" every time he and Del remember their mother in "The Yellow Peril".