Hi Romayne - I feel for you, and I also feel quite strongly about what some people have posted on here. First thing's first - has he seen a doctor? If he really doesn;t see the point in living then he needs to see one asap.
secondly - he needs advice, guidance, support. the absolute last thing he needs is to be told what kind of life he wants. hell if he doesn;t know what kind of life he wants how on earth does anyone else? least of all a bunch of mners who've never even met the lad.
I would really urge you not to push him in any particular direction (all this he must have profession, be part of mainstream society, be in London stuff I find, frankly shocking). The only place you'll push him is away from you.
There are a million ways to be happy - the key is finding the one for you. You have to give him the love and support to help him find it. you can't do it for him. I would say the most you can do is suggest he makes himself a plan - set some goals for the next year or so. his goals might be: get himself to a doc to see if he's depressed, get himself better enough that he can work - he might not need a profession but he does need a job (Are you supporting him (financially) at the moment? He needs to know that that won;t continue indefinitely.) make some decisions about where he wants to live (which comes first - where he wants to live or what he wants to do? he needs to decide).
I'm actually quite angry at some of the stuff said about charity/voluntary work and mainstream society. and as for an Oxford boy needing to go to London....unhappiness in life is often about lack of control, putting people into boxes, people dong what they think they "should " do...
Another thought - Does he have a partner btw? is he nursing a university/first big relationship broken heart?