What you will need: 12 torches, 1 roll of sellotape, 1 dark cape or blanket and 1 tub of hair gel.
Step One: Turn all of the torches on. In the style of a suicide/illumination vest, attach six of the torches to your torso using the sellotape. Attach a a torch to each thigh and shin and one to each forearm.
Step Two: Cover yourself in a thick dark blanket or cape.
Step Three: Break into your girlfriend's house in the dead of night.
Step Four: Unscrew any lightbulbs that may exist inside the room (Not the ones inside your torches).
Step Five: Remove the cape/blanket.
Step Six: Scream very loudly.
Step Seven: Once your girlfriend is awake, calmly say the words "Be not afraid". This will help her to not be afraid.
Step Eight: Once you are 100% sure that your girlfriend is not suffering from fear, say the following words:
At this stage your girlfriend will be 70% certain that you are a ghost. The light coming from your torches will have created an otherworldly spiritual glow, like that of Patrick Swayze in the final scene of the popular sad movie 'Ghost'.
Step Nine: Turn to leave. Just before you get to the door, reach into the tub of hair gel, take out a handful and rub it on the handle. Exit the room. Close the door.
Because of the 30% doubt that you might not have really been a ghost, your girlfriend will now attempt to follow you. To do so she will need to activate the door handle. Upon doing so she will find her hand covered in what she will instinctively mistake for ectoplasm (the sweat of ghosts). All doubt will now be erased from her mind.
Step Ten: Leave the country forever. Your girlfriend will not try to contact you or experience sadness because she will know that you have gone to Heaven; a wonderful happy place that has no phones.