With and Without, Victory Gardens Theater.

The central crisis is soapy: when Jill’s husband doesn’t join her and her married friends Mark and Shelly at the lakeside cottage they share, Jill flings herself into adultery with Glen, the equally lonely and imperfect stranger she brings back to the cottage. To complicate matters, Mark and Jill are old flames, and Mark still feels guilt over extinguishing that blaze. His rage at seeing Jill use the cabin for a tryst can’t disguise his remorse over knowing that Jill had to settle for a marriage much less happy than his blissful union with Shelly. Fortunately, savvy playwright Jeffrey Sweet handles this steamy story and the situational ethics with maturity and wisdom.

At the risk of expanding a sturdy sketch to 90 minutes, Sweet painstakingly explores the situation from all sides and with raw sympathy. He refuses to indulge any wish the audience might have to punish Jill’s philandering, and he wisely weighs the cost of the lies that Mark and Shelly must tell to protect Jill’s shaky marriage. Clearly no easy answers can come out of this weekend because, as usual, sex messes up what it doesn’t consume.

Sandy Shinner’s staging is as sensitive and sage as the script, underplaying the small talk but not the revelations, which speak volumes. Linnea Todd in her sly smile displays Shelly’s knowing competence and flawless tact, which give her a moral and psychological edge over James Sherman’s brittle, defensive Mark and Annabel Armour’s acerbic and ultimately miserable Jill. (But, lacking a chemical explanation, Jill still suffers from too many mood swings.) Marc Vann has a dignified interlude as the divorced ex-con who shows Jill a little unconditional love.