Hello I noticed that you wrote in lots of places, you must be very upset. Please try not to panic. Some survivors can have problems after birth but I don't think it is 'most'.
My surviving son is now 16 months old and we are fortunate to have no problems at all. Your baby is very young and it is hard to tell how they will develop until they become older. But remember that many children who were never twins, can have problems.
Try to enjoy these first few months. remember that most of us mothers and fathers have been terrified and worried about our surviving twins. You are normal.
Best of luck - you can always post on here on days when you feel worried or sad