On the eve of Christmas, when it is so beautiful outside, invite your the only love for a picnic, without telling her about your destination... Give her a ride to someplace with many trees decorated with white lights...As soon as you get there make sure that the lights are turned off. Light some candles, roll out a blanket, have a sit. When you feel the moment is appropriate turn on the lights. If you have done everything right, take my word, she will be stunned. Little by little things will get real cold and then you take out the other blanket (of two you have packed) and you just sit there cuddling, and who knows...