Lennon Parham and Jessica St. Clair Lennon Parham and Jessica St. Clair

Art imitates life on the new NBC sitcom Best Friends Forever, which was co-created, written and stars best friends Jessica St. Clair and Lennon Parham.

"Lennon and I spend, like, 12 hours a day together, more than I have spent with any man or woman," St. Clair told reporters recently on set. "I would say this is the healthiest relationship I've ever been in."

That friendship is the basis for the comedy, which debuts Wednesday. Three years after getting married and moving 3,000 miles away, Jessica (St. Clair) moves back in with her best friend and longtime roommate Lennon (Parham) when she is served divorce papers.  Jessica is startled to see she has been replaced, sort of, by Lennon's live-in boyfriend, Joe (Luka Jones).  "This show is really about what do you do when you have to share your friend for the first time," St. Clair says, "which is kind of a hard thing for women because all through your 20s you are each other's No. 1, and then this guy comes in and ruins everything."

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In real life, St. Clair and Parham met 10 years ago at the Upright Citizens Brigade Theater in New York City (they were wearing similar sweater sets, natch). Because there were so few women performing at UCB at the time, the few rarely performed together. "We were just sort of admirers of each other," St. Clair said.

St. Clair had a male writing partner before she and Parham teamed up to write an HBO pilot, and then what-would-become the Best Friends Forever script for NBC. "I wasn't really able to delve fully into girl porn, which is, like, scenes about Steel Magnolias," St. Clair said. "That means Lennon has to play all the men in my life [when we improvise]. She has to play my ex-husband. She has to play my current love interest. It gets really heated in there."

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The show gives the duo to do some Steel Magnolias material, including their best Shelby impersonations, but both women tplay against their normal type. "I'm always the weird one. [Jessica is] always the b---- and then there's a nice girl," Parham said. "The b----, the weirdo and the nice girl aren't really usually friends, so we wanted to do a show about two real friends," St. Clair said. "But it doesn't have to be cheesy. It can still be wildly funny."

Both say their characters are "exaggerated" versions of themselves. However, St. Clair admitted she did steal the premise for the show from her own life. (This story, thankfully, has a happy ending. Five years later, her best friend's husband is "like my brother," she said.) But has working together affected Parham and St. Clair's real-life friendship? Not at all. "When we went away for Christmas break, I thought, 'Finally, Lennon and I get some time away,'" St. Clair said. "We literally spoke, texted and sent pictures. It's an obsessive, unhealthy relationship in that respect."

Best Friends Forever premieres Wednesday at 8:30/7:30c on NBC.