Isn’t it romantic? Infidelity, that is

Warning: Seeing other people in the interval leading up to your wedding can be hazardous to the relationship.

Although it takes the couple in the film “Seeing Other People” 90 minutes to learn this rather obvious lesson, fine performances from some TV-friendly faces make this slight romantic comedy more enjoyable than it sounds.

Julianne Nicholson (“Ally McBeal”) and Jay Mohr (“Action”) play a young couple planning their wedding after living together for five years -- who disastrously decide to have what used to be called an open relationship.

Alice does some type of nurturing work involving plants, while Ed is a TV comedy writer. Their circle of friends includes Alice’s rigid sister Claire (“Gilmore Girls’ ” Lauren Graham), Claire’s lecherous British husband, Peter (Bryan Cranston of “Malcolm in the Middle”), Ed’s cynical agent, Leo (Josh Charles of “Sports Night”), and their sensitive pal Carl (Andy Richter of “Andy Richter Controls the Universe”).

At her engagement party, Alice accidentally witnesses a friend having a quickie with a waiter and begins to question her own limited sexual history. She suggests to Ed that until they’re married they both be allowed to have a series of meaningless flings. He is initially skeptical but agrees when he figures his “good girl” fiancee won’t go through with it.

Well, Alice does go through with it and likes it. A lot. The fling has Alice feeling frisky and also has a surprisingly erotic effect on her and Ed’s sex life. After some hesitancy and a few false starts, Ed begins to participate willingly, wooing and bedding a string of actresses and waitresses.

Of course, the bacchanal can’t last, and the expected complications set in. The usual discussions about love and trust occur, followed by the predictable recriminations before the loving couple comes to the conclusion that this was a really bad idea.

None of this ultimately adds up to much, but it is fun to watch Graham and Richter play against type, and Nicholson, who gave a terrific performance in the 2002 indie drama “Tully,” gives the movie some needed heart. As Alice, the actress dives into an unconvincing premise, bringing to it an appealing mix of naivete and disappointment, reveling in her sexuality as she tiptoes about trying to avoid the inevitable hurt feelings. Alice is as melancholy that her newfound broad-mindedness doesn’t work out as she is that her relationship with Ed has been tarnished.

Husband-and-wife team Maya Forbes and Wally Wolodarsky, who began their careers writing for TV, co-wrote the screenplay. Wolodarsky directed.

Along with the performances, there is a languid truthfulness in some of the dialogue that keeps “Seeing Other People” from being one of those completely forgettable indie romances that play in perpetuity on cable. The story, however, doesn’t take any real chances and leaves the characters with little to do apart from sitting around accepting what is blatantly obvious to the audience from the word go.

*

‘Seeing Other People’

MPAA rating: R for strong sexual content, language and some drug material.

Times guidelines: Some nudity and a frighteningly large sexual appliance.

Jay Mohr...Ed

Julianne Nicholson...Alice

Lauren Graham...Claire

Bryan Cranston...Peter

Josh Charles...Lou

A Pariah presentation, released by Lantern Lane Entertainment. Director Wally Wolodarsky. Producer Gavin Palone. Executive producers Vivian Cannon, Maya Forbes, Dan Kaplow. Screenplay by Maya Forbes and Wally Wolodarsky. Cinematographer Mark Doehring-Powell. Editor Stewart Schill. Costume designer Jacqueline K. St. Anne. Music Alan Elliott. Production designer Dan Butts. Running time: 1 hour, 30 minutes.

In limited release.