When I was young I was quite happy to be an only child, plenty of friends and cousins and I had a wonderful childhood. As an adult I have missed having a sibling, missed out of nieces and nephews, my children have missed out on aunts or uncles and cousins. The first time I began to miss a sibling seriously though was when my dad died.
However, I was also determined to have a large family. When that was not possible I adopted a family group of 4 children, and now they are adults I am a foster carer so the house is always full.
However, my mum has recently become very unwell, and I feel the burden of being the only child overwhelming. I wish so much for someone to talk to who would understand and share the responsibility and decision making over my mum's future care. I wish there was someone else to visit her, so (selfishly I know) I could have a day off. It is now the greatest sadness of my life, I just wish there was someone else to be there for my mum too.
I also too feel totally and completely bereft at having no biological link to anyone. Knowing that with little time left for my mum, I (even though surrounded by husband, adopted children and foster children) I will be alone. With that also comes a huge sense of grief and guilt at being the very last 'of my kind'.
Sorry, I though I would answer this from the heart....it's now very, very lonely being an only child.
I wish you will, OP, no matter what you decide.