A World With You - M. Roca

How far would you travel to find 'The One'? When chronically indecisive maths teacher Gemma Higgins accidentally enters another dimension, she learns the great secret of existence: that we inhabit a multiverse run by giants, HR managers and angst-ridden writers. Unable to return to her old world, Gemma is told she can take her pick from one of her remaining lives. She chooses a life where she meets 'The One', and is delighted when it seems 'The One' is the ex who shouldn't have dumped her. If only she could stop being distracted by the handsome ghost she's been able to see ever since she arrived from the other dimension...