What a lot for him to shoulder for such a young age, but you must be so proud for him dealing with it in a mature and adult way.
Like the poster above, I found out I was pregnant at 35 weeks!!! no bump, don't have monthlys due to pcos, no symptoms at all and we were not expecting it because we were told a while back that we would never be able o have any more kids.
I ate all that I wasn't supposed too, drank, smoked, fell out of the bath directly into my stomach, and lots more besides.
I think you must be a fab mum to have such an honest and open relationship with your kids and the only thing you can do is support him as much as possible.
Try not to feel to bad about him being in London dealing with it all as it may well be good for him in regards to 'the world owes me everything'
Above all else, as you say whats done is done and it can't be changed, Try to see things positively, for instance you are still young enough to play and help with the child if necessary. He will learn so much from you over the coming months and it you will probably see him grow from a boy to a man (as hard as that can be sometimes!!)
I hope everything goes well for you.
If you fancy a chat at any point off the boards with someone who has been there (daughter was pregnant at 15) please feel free to emaail me
slightlymad1@hotmail.co.uk