GUYS I JUST HAD A REALIZATION!!
I don't know if this was obvious to other people but when Rio said " I've got a scar" and Agatha goes "No you don't", it's because Rio is death!! And her skin probably never ever gets scarred it just regenerates or something—unlike human skin. She licked Agatha's palm, and healed it so it makes sense how she would not have physical scars. So Agatha says that because yes, true, Rio is death therefore no, she does not have physical scars. And maybe, Agatha didn't want anyone to realize she's different (death) so she says "no you don't" to try to shush her ass. But Rio came through with an even BETTER bonfire story: a lifetime emotional/mental scar she carries as her burden from when she hurt someone she loved a long time ago. Which left a big, unhealed scar indeed. Exposing Agatha's past, but also humanizing her in a way. Maybe, she was hoping to make the coven realize how caring Agatha is after the last scene where she cries about Billy. Triggered by the begging, it prompted Rio to probably do justice for the both of their stories by giving the others a backstory, a little context if you will. But also to sort of confront Agatha about their past.
"Why do you let them believe those things about you, hmm? About Nicky?"
"because the truth is too awful".
It's awful in the sense that they were doomed, from the beginning. It's a tragic love story. And after being hurt by her mother, she probably never wanted to tell anyone she is a coven-less, queer witch.
I personally think, the truth was not as awful as the lies they spread about her and fuck— about Nicky's death. How she exchanged him?? Like I don't know why she stayed quiet about that. The pain is too great. Rio literally gave him the calmest death, leaving Agatha to grief and seek revenge on other witches because she didn't know better.
I can analyze this forever but I just woke up.
I'd LOVE to hear everyone else's 2 cents.