Things are about to get crazy on “Crazy Ex-Girlfriend.”

Sure, when the show debuted in 2015, Rebecca Bunch (Rachel Bloom) quit her job at a New York law firm and moved to California to win the heart of Josh Chan (Vincent Rodriguez III), whom she had a crush on when they were teens.

But Josh left Rebecca at the altar in the Season 2 finale to join the priesthood. As Season 3 begins (Friday, Oct. 13, 7 p.m., CW/Ch. 30), hunky-but-simple Josh will be on the rebound and trying to make a go of it with … God.

“Because he loves Jesus. And Christmas,” Rodriguez said with a laugh. “Josh’s simplicity leads him down that path, thinking he’s doing the right thing.”

But Rebecca will be out for revenge as the show finally grows into its title.

“If you thought this show was going to be funny ‘Fatal Attraction,’ that’s what we are [in Season 3],” Bloom said. “Rebecca thinks that she is a woman scorned.”

Not that she’ll be all that good at it. Josh isn’t going to come home and find his pet rabbit in a pot on the stove.

“If Rebecca tried to boil a bunny, she would take the bunny and be, like, ‘Oh, it’s so cute,’ and bring it home,” said executive producer Aline Brosh McKenna, who co-created the show with Bloom. “A month later, she would have 50 bunnies. So she’s not very good at trying to be the femme fatale.”

Right off the bat, Rebecca comes up with a plan that’s, yes, crazy. And her friends are afraid to tell her how crazy it is. But, eventually, she is going to confront her mental-health issues, which are not insignificant. And do it in a way the character — and the show — could not have attempted in Season 1 or Season 2.

“We’ve taken two years to earn the right to lean into our title of ‘Crazy Ex-Girlfriend,’ ” said Donna Lynne Champlin, who stars as Rebecca’s best friend, Paula.

Season 1 was more of a “traditional romantic comedy” in which you “protect the lead by having someone else” — Paula — “be the engine of chaos,” said McKenna. In Season 2, Rebecca became “a little bit less of that clumsy, hapless, romantic comedy heroine.”

We’ve always known she had mental-health issues; in Season 3, Rebecca will deal with them. And as she figures out what’s wrong with her, “Everyone else is forced to see what’s wrong with them,” Champlin said.

Including Josh, who’ll be forced to face his shortcomings. “And what’s weird is that Rebecca is going to actually help facilitate that, given her revenge-seeking bullet [aimed at] me,” Rodriguez said.

Each episode still features original musical numbers, and they’re better than ever. So is “Crazy Ex-Girlfriend” in Season 3. I’m already hoping The CW orders Season 4 and allows Bloom and McKenna to complete the series.

Season 4 would be “a very distinct chapter,” Bloom said. “That’s why we’ve always said [it’s a] four-season show, because we are telling a finite story of a point in a young woman’s life.”