We have one DD who has SLD, severe autism and suffers from a life threatening form of epilepsy.
We only ever wanted 1 DC and she took 4 years of infertility treatment and several missed MC's before she finally arrived but unfortunately suffered a devastating condition at 7 months old which left her with her lifelong difficulties.
Things were incredibly tough when she was very young primarily, we later discovered, due to her being prescribed the wrong medication. DD had to attend special needs boarding school from 8 years old as the specialist day schools couldn't cope with her. This was devastating initially for us but we visited her every weekend and long term it proved to be a Godsend.
To cut a very long story short, DD is 30 now, lives in her own beautiful apartment in an excellent, small managed centre close to home and the three of us have an incredibly close bond. We haven't had the normal parenting experience by any measure e.g. no first days at school, no exams, no relationships, no university, no career concerns, no housing stresses etc.
However, what we do have is a beautiful DD who will forever be like a 3 year old and who is the centre of our world.
My advice, should you choose to stay with the 1 DC, would be not to compare with friends'/family children but to focus on what you DO have. It does sound as if your ds is much more capable than our DD ever was or will be
but I can honestly say we have never bothered about what we didn't experience or fret because we will never have grandchildren. Our lives are unique, our DD is unique and when we see how happy and confident she is now, in her own world, we know we did the best for her and she loves us unconditionally.
I wish the very best future for the three of you.