Okay, gotcha.
I would maybe suggest doing a bit of promotion/recruiting to increase your student base, and possibly focus on getting some adults in their 20s or 30s to add a different sort of energy to the classes.
I would also echo the sentiments of the other posters who said that it might be worth taking some time to learn a new martial art. I think the human psyche is such that we need variety in our lives. If you focused on learning something else then that might re-ignite a passion for martial arts in general and after getting a little "space" from TKD when you go back to focus on it you might feel renewed.
I would also agree with those who said that the social factor is a big part of martial arts. Personally, I think this is true for most activities. Sometimes fulfillment comes not so much from what you do, but who you do it with and the experiences that you have with those people.