I Do … Until I Don’t Lake Bell, Ed Helms, Mary Steenburgen, Paul Reiser. Directed by Lake Bell. Rated R. Opens Friday at Green Valley Ranch and Suncoast.

In 2013, actress Lake Bell made her feature-film debut as a writer and director with In a World …, a funny, intelligent and warm romantic comedy about a voiceover actress making her way in the cutthroat world of movie-trailer narration (while also navigating her romantic troubles). It was a promising filmmaking debut for Bell, who remains a familiar face in movies and TV shows, usually in comedic supporting roles. So there was every reason to be optimistic about Bell’s second effort as a writer and director, another romantic comedy with a title featuring an ellipsis, I Do … Until I Don’t.

But I Do fails in so many of the ways World succeeded that it’s almost hard to believe that it was made by the same person. Instead of a unique setting, I Do takes place in the generic suburban sprawl of Vero Beach, Florida, where bland people lead bland, vaguely dissatisfying lives. In particular, married couple Alice (Bell) and Noah (Ed Helms) run a failing window coverings store, are struggling to conceive a child and don’t seem to like each other very much. Along with two other couples, they’re recruited to participate in an anti-marriage documentary by British filmmaker Vivian Prudeck (Dolly Wells), who’s determined to bring down the whole institution.

One of the other couples in the documentary is Alice’s hippie sister Fanny (Amber Heard) and her free-spirited partner Zander (Wyatt Cenac), but the third couple, realtor Cybil (Mary Steenburgen) and her husband Harvey (Paul Reiser), has no connection to Alice and Noah, and Bell struggles to bring all the characters together in her disjointed narrative. It doesn’t help that they’re all irritating whiners, with clichéd problems that Vivian exploits in obvious, narratively convenient ways. The unfunny comedy hinges on contrived misunderstandings, and none of the emotional arcs are convincing in the slightest. The couples are all completely dysfunctional until they conveniently aren’t, for the sake of wrapping up the story, and then the story limps along for another 20 minutes anyway.

Bell has put together a talented cast but has given her actors poorly written characters with insufficient motivation, and the performances rarely rise above the subpar material. The framing device of the documentary adds almost nothing to the couples’ stories, and Bell shoots the documentary interviews with erratic, artsy close-ups as if Vivian herself knows nothing about filmmaking. Despite its leading title and the provocative ideas of some of its characters, I Do turns out to be surprisingly prudish, ending by celebrating conventional relationships and mocking the idea of any alternative approach to marriage. It’s about as clever and sophisticated as a late-period Garry Marshall movie.