Meanwhile, on a work surface, cut the bottom and top off the grapefruit so that it sits flat on the cutting board. Cut away the peel and pith of the grapefruit down to the flesh. Over a bowl, slide a knife between each membrane to remove the segments and to catch all of the juice. Cut each segment into three pieces and add to the couscous. Add the honey to the bowl of grapefruit juice and mix well.