Stage Kiss at Hampstead Theatre: Amusing backstage comedy

Anyway, in scene two Buring’s character’s actual co-star in the first play appears and, uh-oh, it’s the guy she had a fiery fling with when they were young, poor actors starting out, which ended acrimoniously. He never married or had kids and is now shacked up in a slovenly apartment with a supposedly saintly, younger schoolteacher. Their first stage kiss is awkward. Their fourth or fifth is also awkward, but for different reasons. Trapped in a doomed production, will they succumb to temptation and destroy their offstage lives? Take a wild guess.