I am a namechanger, fairly long-standing poster, don't want situation recognised in outside world as yet.
DS1 - 17, 18 in 5 weeks, is about to voluntarily withdraw from the RAF - he has been in basic training for 4.5 weeks, and this week has basically emotionally broken down and decided he can't handle the self-sufficiency or pressure. His training according to his Flight Staff is going extremely well, and he is reaching a high standard - no concerns at all apart from a couple of ligament strains which are extremely fix-able.
We had no inkling anything was wrong until Thursday when he rang me in floods of tears and sent an extremely emotional text saying he can't do it any more etc. He has been home for the weekend, partly on compassionate grounds as he has been put back a couple of weeks for failing a test as he was resting in the medical centre at the time (crying, vomiting, etc) Over the weekend, he is citing some briefings he has had as the main reason, apparently they have drummed into them from day one that regardless of the trade they have chosen (in his case aircraft maintenance) they have a high chance of being put on the front line to fight or be expected to travel 'in theatre' and be at risk of being blown up by an IED. He WAS aware he is a soldier first - no-one could have done more preparation or research since the age of about 13 than him into all it entails, this was all he wanted and there was no 'Plan B', however they have basically made him think he is at high risk of being severely disabled or worse, regardless of whether he is anything from regiment to a chef.
Anyway, the ins and outs are irrelevant. We have spent 36hrs going over everthing, and it just makes him more resolute to pull out. But what now?? He is almost 18, with only GCSE's and an NVQ in Public Services, he quit sixth form when his RAF application was at a very advanced stage and the school wouldn't keep him on basically as he wasn't commited, He has a reasonably good list of vocational accolades including his D of E gold - but in this climate, what chance at all has he of finding any sort of job, when, basically, he has quit school and his first job? DH will not entertain the idea of him going to college - he has missed the enrolment dates anyway, and is insisting he goes all-out to find work, but in the same breath insists there are absolutely no jobs out there for teens, especially ones who have a history of unreliability. 
We both feel he is making an enormous mistake - this is an unparalleled oportunity with concerns which he is refusing to put into context. We also feel that the girlfriend is a not-insignificant factor but he denies this.
I am absolutely devastated for him. We thought the future was going in one direction, and in a few short weeks and completely out of the blue, it has taken the completely opposite direction. Whilst I can see DH's point of view, it doesn't solve anything and I am frightened, quite frankly, and confused.