You know that sinking feeling when you look around and realize that all your friends are married or in serious relationships? Joshua Harmon heads for this lonesome place from the very beginning of his frightfully funny relationship comedy, “Significant Other.” Trip Cullman helms his flawlessly cast ensemble through laughter and tears as all but one of four friends finds the right mate. The lone outcast is the youngish gay man deserted by his dearest girlfriends. As played by the irresistibly lovable Gideon Glick, you want to fix him up or take him home for yourself.

It’s all about growing up, you understand, for a generation that has done its best to live in a state of perpetual adolescence. Bold-as-brass Kiki (a petite tyrant in Sas Goldberg’s rollicking performance) is the first to take the plunge into self-actualization. (“I just stopped thinking about other people and I got to this place where it was all about me.”) Some poor guy took the bait, and nobody had the nerve to warn him to run for his life.  Costumer Kaye Voyce nails Kiki’s vibrant personality perfectly with the hot pink feather boa and the tiara she wears to her bachelorette party.

Voyce also does a neat job of defining Vanessa — so clever, so articulate, and oh, so clinically depressed. Vanessa’s color is black, of course, and as played by Carra Patterson, she’s elegantly fashionable in her own languorous way. (Vanessa is the one who suffers most acutely when forced to wear the hideous bridesmaids’ gowns chosen by her friends.)

The true bests in this group are sensible Laura, a generous friend in Lindsay Mendez’s selfless performance, and sensitive Jordan, kind and loving, but so very vulnerable as played by Glick. They are true soulmates, these two, and in fact were roommates until recently, when Laura sensibly reminded Jordan that, having reached their late 20s, they are officially grown up — “and grownups live alone.”

Harmon, who used an abrasive comic voice in his domestic drama “Bad Jews,” writes in an equally intelligent but more bittersweet vein here to convey Jordan’s conflicted feelings of terror (of being left alone and unloved) and longing (to find a mate of his own).  “I know life is supposed to be this great mystery,” he says. “But I actually think it’s pretty simple: find someone to go through it with. That’s it.”

If only he wouldn’t fall for unattainable dreamboats like Will, the hunky guy from work played by John Behlmann.  (Along with Luke Smith, Behlmann also shows up in the roles of the girlfriends’ various suitors.)  Harmon has written himself a genuine Everyman in Jordan, who is never more relatable than when he writes Will a lovesick and highly inappropriate email — and then dithers in agony trying to decide whether or not to hit Send.  Straight, gay, or otherwise, who among us hasn’t written that letter?

Not to worry about Jordan, though.  His loving if slightly doddering grandmother played by the wonderful Barbara Barrie (let it be said once again that this is really a well-cast show) gives him great advice when she reminds him that life is a very long book — and while this moment may feel like the end of the world, it’s only one of many chapters yet to come.

Off Broadway Review: ‘Significant Other’

Roundabout / Laura Pels Theater; 405 seats; $79 top. Opened June 18, 2015. Reviewed June 17. Running time: <strong>TWO HOURS, 15 MIN.</strong>

  • Production: A Roundabout Theater Company production of a play in two acts by Joshua Harmon.
  • Crew: Directed by Trip Cullman. Sets, Mark Wendland; costumes, Kaye Voyce; lighting, Japhy Weideman; sound, Daniel Kluger; choreography, Sam Pinkleton; production stage manager, Samantha Watson.
  • Cast: Barbara Barrie, John Behlmann, Gideon Glick, Sas Goldberg, Lindsay Mendez, Carra Patterson, Luke Smith.