Hiya!
Its quite normal to feel this way. I am pregnant with my 2nd child and have had a wobbler or two, I have asked myself & worried about every scenario possible! I've even wondered WHY I wanted another, as my little boy is my world world plus more. But at this stage its hard to see past my pregnancy, I was the same when pregnant 1st time around - I couldnt picture the end result so to speak.
My little boy enriches my life more than anything, and the last thing I would want to do is hurt him /betray him. Having a sibling is such a precious gift to any child, and I know my son will benefit in so many ways. I am prepared that he may feel a little put out at first but I will do everything within my power so that he knows just how much he is loved, so hopefully the adjustment wont be too bad for him.
The betrayal thing is normal ie you ask yourself if your first child isnt enough, as why do you want another?! We all know thats not the case at all though. Our children are always good enough and fullfill is more than anything - its part of nature and part of life and we shouldnt have these emotional battles as common sense tells us what is right.
Do remember though that your little girl is still a baby in herself, and when the time is right you will just know. I know that my son is ready for a friend as such. He will be nearly 3 when we have our 2nd child and nearly starting nursery. It took me a long time to come around to the idea of having another child, and now I am pregnant I am so exciting about family life changing again. As the years go by, my son will have a brother or sister which is something I always loved. I have lots of siblings, and I am so grateful for them. They are my friends into adulthood and always around when I was little, as a friend, as company - even someone to snitch on. Its all good, try and think of things this way and you'll be fine
Sorry I have waffled on havent I?!
Take care x