Well, why can't you have some fun too while he's away on his gap period? You're only 18 and the two of you are not joined at the hip. Use the opportunity to do something different, develop a new hobby, get fitter, read some interesting new books, get a part-time job. The list is endless.
Keep yourself busy and involved and before you know what has happened the 6 months will have passed and he'll be back. If you're sitting at home depressed he'll feel emotionally blackmailed and guilty about going away and won't want to come back to you.