She shatters his comfortable picture of the world.
Candice's appearance is the moment when the viewer first seriously questions Joe's words. Before that, he seemed slightly toxic, but still "not that bad." Candice breaks that myth. She says, "He did the same thing to me. And he can do it again."
The irony is that Joe still sees himself as a victim. He justifies himself:
"She manipulated me."
"It was all because of her cheating."
"I was just defending myself."
But the more actively he makes excuses, the clearer it becomes: his story is not a drama about love, but a chronicle of violence.
Candace's function is in storytelling:- She flips perspective: we now see that Joe is not just a "suffering romantic" but a recurring predator.
- She launches the show's theme of payback, even if that payback doesn't fully come.
- Her appearance is an intrusion of reality into Joe's fictional world, and that's what makes season two so tense.
Candice isn't just an ex. She is a symbol that the past cannot be erased, that behind every beautiful fantasy there is a trail of destruction. And while she doesn't become a triumphant heroine, her voice is important: it reminds the viewer that this is not love. This is a cycle of pain.