Sending prayers and positive vibes. I hope he will accept some help with adjusting to all the changes he is experiencing. This in NO way means he is a failure, though it likely will be hard to convince him of this. It actually means he is smarter than the average and that he is far more in tune to what he needs. Both of those are more reliable predictors of success than grades or test scores.
College retention studies have shown that students who take a gap year, or year off between high school and college usually get better grades, learn more and can apply what they learn/know more effectively, and get better jobs that earn more money once they graduate from college. My mom spent around 10 years on the retention committee for our local university, so this was something we read and discussed over dinner, etc... (yes, were a bit odd. What did you expect from MY family? LOL). By coming home your son may have ma on of the best decisions he could make for himself. Going to college in a year or so, when he is ready, will do TONS more for him than going now when he is miserable, scared, and simply not ready.
One key factor in making this a wise choice is what he does with his gap year. Working, esp if he can get a toe into whatever field he wants a career in, is important. Dealing with any medical and/or mental health issues is important during this year also. Sitting around playing video games, watching tv, etc... is NOT a wise way to use this year. If the family can afford it and he wants to do this, it could be a good year to travel or work on a cruise ship or do something similar. Just my 2 cents.