The writing style matters a great deal. A vivid and engaging writing style can bring the story to life. Descriptions of the settings, like the Red Keep where they interact, and the emotions of the characters, whether it's Cersei's resentment or Robert's longing for a different kind of relationship, should be detailed and immersive.
If Robert Baratheon loved Cersei, it might have changed the course of many events. Their relationship could have affected how they ruled, and potentially influenced the fates of other characters. Maybe there would have been more harmony within the royal family.
If Robert Baratheon married Cersei in fanfiction, it's possible that their children's fates would be different. Also, it might affect the alliances and rivalries among the noble houses. The story could take many unexpected turns based on this alternate setup.
You can try searching on popular fanfic platforms like Archive of Our Own (AO3). It has a vast collection of fanfictions, and you might be able to find some good Cersei x Robert fanfics there by using the search bar and relevant tags.
It could have led to a very different power dynamic in Westeros. Maybe Robert would have been more controlled by Cersei, or their relationship could have sparked more political upheaval.
Well, for one, the Lannister influence might not have been as strong. Also, the fate of Robert's children and the succession to the throne would likely have changed drastically.
The son's character might develop as he uncovers family secrets. Knowing about his mother's true nature and his father's misdeeds could make him question his own identity. He could start as a naive young man, but as he digs deeper, he becomes more cynical. But instead of being consumed by it, he decides to break the cycle of corruption and lies that his family has been part of. He could start to develop his own moral code, different from the cut - throat ways of his parents.
One possible plot could be that their son discovers the truth about his parents' tumultuous relationship. He might struggle with the knowledge that his mother had affairs and his father was not the ideal man he seemed. This could lead him on a journey of self - discovery, trying to figure out his place in the Seven Kingdoms.