Hi M.!! I wasn't going to respond to your post, because I figured you were already getting plenty of advice, but then I read through all of the posts and realised something...every one of them stated negatives about only children!! It's as if all of these parents think that only children are freakish and unnatural. Then I noticed something...not one of them was an only child...go figure!! Well, here's my two cents on being an only (freakish as that may be) and having an only (again..freakish, I know!!).
I had a wonderful childhood. I was extremely loved and I can only recall yearning for a sibling for a very short period. I got over that when I spent lots of time with my best friend and her very annoying younger sister. I was blessed with having close cousins (many of whom were only children as well) and we were able to play together and then go home! I don't feel as if I grew up too quickly...I never had to compete for my parents attention...I didn't have to worry about who they loved more...ever! I do feel that being an only made me more creative and in touch with myself. I have never been afraid of spending time by myself, and I am very in tune with nature, my surroundings, animals and, yes...other people. Being an only does not make you anti-social!
My daughter is an only. She is 14 months old is very social and well adjusted. When she interacts with others, she shares just as well as any other 14 month old (i.e. not very well). The only difference I can see is that she is not aggressive towards other children, whereas it seems as though every child we know that has siblings is aggressive towards other, younger children.
My husband and I decided when we found out we were going to have a baby that we didn't need to personally contribute to the population explosion. He and I are both only children and felt that it would be a wonderful way for our little girl to grow up.
Just some thoughts from the other side of the fence. There are good things and bad things about either decision. Just don't let anyone else pressure you because they think you have an obligation to have more than one child. You don't!! Love the child you have. Love the life you have. If you chose to add to that, do it because YOU want to!! Good luck...