Layla17, I do think your partner is having a major wobble at this time. New house, needs doing up, young family, sick child, you away from friends and family, its SO much STRESS!!!! Do you think that he has been affected by your younger childs birth and maybe he has been left drained with worry?
IMO, I think you should tell him A.S.A.P about the pregnancy during a relate session because as one poster said, he might find out at a later date. The councillor can mediate and guide the session and this is too much for you to deal with on your own.
You have got to think about youself a bit more now and like other posters have said, take care of yourself, mentally and physically.
You say that you cannot cope without him, what facts do you base this on?
From how I see it,you are:
strong enough to get through this last year not knowing if your child is brain damaged
strong enough to move away from friends and family
strong enough to take on a house that needs major work
strong enough to contemplate dealing with this pregnancy on your own(just for now?)
Strong enough to share your problems with complete strangers/mners.
Come on kid, you can do this.