justine miliband , right , said ed , left , did not tell her that he was in a relationship when they first met at a party .
the labour leader at a dinner party hosted by a mutual friend and thought he was ` good looking ' and ` unattached ' .
but the labour leader failed to tell his future wife that he was secretly going out with their ` mutual friend ' - understood to be the former bbc economics editor stephanie flanders .