This is another trophy/achievement that is only in the original version of the game, and not the Definitive Edition. As you complete the Drustan Trials, you will be able to make a wish. One of the wishes is to marry Gemma, so pick it and head back to Cobblestone. You can find Gemma at your house, so speak with her there, then go to bed, with the trophy/achievement popping upon waking up.