pussollini, I think you are being hard on yourself; and I also think that the few posters who are being hard on you cannot have had much experience of a demanding teenager.
I love both my boys very much. I quite often do not like DS1, who has behaved very, very badly over the past couple of years, and can still be a pain. I delight in the company of DS2 most of the time, who is clever and articulate and funny. And yet... Every single evening after we have sat down and eaten a meal together, I need half an hour or sometimes more by myself - I really need it - or I get grumpy and shouty and cannot cope with them at all.
Luckily for me, they go off of their own accord (almost always) and amuse themselves. If they hung around me, demanding more of my attention than I could give, I think know I would not cope.
I get a bit stir-crazy if they are ill, too. The more clingy they become, the more I want to pull away. I know it comes from the fact that I am a single parent, and there isn't anyone around to share the care and attention, and sometimes I just reach 'overload'. I do feel a bit guilty, but I also accept that I'm only human: if you are giving and giving most of the time, there does come a point (in each day) when you are just emotionally tired, and you need to re-charge your batteries.
I agree with those people who are saying he is probably insecure and overly-demanding because he's afraid you're going to leave him too. Poor boy. And poor you, too. If he was secure, he wouldn't be hanging around you all the time. It isn't normal. But then, you always knew this wasn't going to be a normal situation.
All the ideas about telling him you'll stick with him no matter what are good ones. He probably needs to hear that. But also, I wonder whether he needs more practice at you going away and coming back to him... I wonder whether you are the person who so far, is always there - are you at home most of the time - the person who he comes back to, but who rarely goes out/away? He probably doesn't experience you 'going away' very often, and given his background, he is understandably afraid that if you do, you may not come back...
I actually think that it is probably very good for him that you go into your room each evening for a while by yourself. It will be hard for him, and it will make him anxious - but each time you do it, and then come back, it will become a little bit easier, because he is 'practising' losing you temporarily, and he is facing his separation anxiety.
I am on very tenuous ground here - not offering advice, but speculating based on my intuitions and experience... But I would suspect that because you feel guilty about leaving him alone, you may be giving him subtle signals that feed his anxiety. Unconsciously he will be wondering why you might be acting guilty... Could it be because you are not coming back? Or because you are planning to leave him soon?

I would suggest that if you can leave him more deliberately and cheerfully, saying something upbeat each time like "Right, I need a bit of time to myself now! See you in half an hour!" he may well begin to find it easier quite quickly, because you will be signalling to him that it's perfectly normal and fine for you to withdraw for a while, and that you're coming back. :)
I may be wrong... As I say, this is just my intuition... But it might be worth a try :)