Although both have apparently moved on to pastures new, both Jack (Gerard Carey) and Ruby (Amy Booth-Steel) are still emotionally trapped in their short-lived relationship. Reunited in a bar, the pair must decide whether to throw away their super-human other halves: in Jack's case a leggy, blonde polyglot with a mortgage, in Ruby's a Canadian paediatric orthodontist who wants her to emigrate to the States.
But the central relationship is tepid, and although references to marriage, destiny, love and pain fill the book there is little emotional foundation. Most of the exchanges boil down to crude jokes about sex and the cheap asides to the audience invoke bad sit-com.
Lorraine's score is pleasant, and it's a nice touch for all-knowing barman Harry (Chris Whitehead) to be the show's sympathetic accompanist, but Ex is handicapped by its lyrics which at times are torturously unimaginative.
Siobhan Dillon and Simon Thomas inject the show's first signs of dynamism at the top of the second act, at last raising a smile and throwing in a tap number for good measure - finally in this "sweet and sour" comedy we're actually having fun. Dillon has the best of the melodies and shows off her range whilst Thomas does a sound job with his torch song.
The show's main failing is that as characters Ruby and Jack pale in comparison with their prospective other halves. Carey isn't the loveable rogue he needs to play in order to get away with the way he treats the women. The idea that there is a thrill to not having any trust in a relationship also rings false, but is on par with a number of the show's other two-dimensional assertions around ideas of love and romance.