Warning: Spoilers for Firefly Lane season 1 are ahead.
Considering how close Tully (Katherine Heigl) and Kate (Sarah Chalke) were for practically their whole lives, the season 1 finale of Netflix's Firefly Lane is jarring. As the pair attend Kate's father's funeral, Kate sees Tully and we learn that at some point between 2003 and 2005, they stopped talking. "When I said I could never forgive you for what you did, what did you think that meant?" Kate says to her former BFF. "Leave. I don’t ever want to see you again."
Prior to this moment, we'd watched as the duo overcame all kinds of hurdles in their friendship and more than one serious fight. Kate even forgave Tully for helping her daughter Marah (Yael Yurman) get on birth control behind her back — which was a huge overstep on Tully's part. Having been friends since they were teenagers in the '70s, they seemed inseparable. What on earth did Tully do?
Ali Skovbye, who plays young Tully, told Refinery29 that she couldn't say much without spoiling a possible season 2. But she was able to point us in the right direction: "I think as strong as a connection is — any romantic relationship or platonic relationship — sometimes life happens, stuff happens. You can't always control it."
There are moments throughout the series where you can see tension building between Tully and Kate that could lead to a falling out. Perhaps Kate just reached a breaking point. As we see in the '80s timeline, Kate particularly struggled with how much attention their news station boss Johnny Ryan (Ben Lawson) paid to Tully. Kate had a crush on Johnny from practically the first moment they met, and though there were feelings on his end too, it took him a long time to act on them. He slept with Tully before he eventually married Kate. Knowing that her friend had been with her husband undoubtedly weighed on Kate, especially since Tully and Johnny remained close. He was the producer on her talk show, The Girlfriend Hour, and would often turn to her when things got difficult in his marriage.
Plus, Kate always felt a little bit less-than when Tully was around — and not just with Johnny. Her parents heaped praise on Tully, but were harder on Kate. Her brother Sean (Jason McKinnon) asked Tully to give a speech at his wedding instead of Kate. He even trusted Tully with the secret that he was gay, and Tully never told Kate. While it wasn't Tully's place to out Sean, it clearly hurt Kate when she found that Tully had known Sean's secret since 1974, while Kate didn't learn it until 2003.
But since they'd always gotten over every other fight — including the kinds of things normal friendships don't recover from — it must have taken something really big to blow their relationship up. The book Firefly Lane, upon which the series is based, offers an answer.
In the Kristin Hannah novel, Tully decides to help Kate and Marah's relationship improve. She invites the mother and daughter on her talk show so they can hash things out. But once Kate is on camera, everything goes wrong. Tully reveals live that the segment is called "overprotective mothers and the teenage daughters who hate them." She also brings in a doctor who essentially tells Kate that she's a bad mom. The whole thing feels like an attack to Kate, and she considers it unforgivable.
It's possible the show will include the same inciting incident, but since it's already changed a lot from the book (including the fact that Tully's not the person whose funeral Kate is attending), the possibilities are endless. Anything could be the reason Kate and Tully eventually stop talking.
Whatever the catalyst, we can be sure it will be made worse by Tully's inability to ever apologise. In those final moments of the episode, Tully seemed confused as to why Kate was still mad at her, as if it never really sunk in that Kate may be justified in being angry. As Heigl told Parade of her character, "I don't even know that [Tully] knows how to admit that she’s made mistakes."
Until — and unless — Tully can own whatever it was that she did, there's probably no hope for reconciliation. But that's a story for season 2.