I think it's the same boy, her husband in the beginning and the lover of her youth.
This is very much a song about change, about growing old. It's the opposition between everything that made them perfect together in their youth -the wildness, the art, the chaos- and the distance between them now: They should be happy, but they aren't. They've aged, matured; he's changed, and because of that, he's the one that got? away. Therefore the ending: Had he died, they would have been perfect forever.
