My best friend is an only child and as a child she loved it, but as an adult she always says she wishes she had a sibling. Her parents are both dead and I think she feels very lonely with nobody to share family
memories with etc.
I have a sister and she made my childhood and teenage years so joyous, we were inseparable. We are adults now and we spend HOURS laughing over all our memories from our childhood. I love being an auntie to her children and she loves being an auntie to mine etc.
I come from a big family as my mum was one of three, my dad was one of five, they all married and had children too so I have 10 cousins and we have lots of childhood memories with them too etc and we are still close with them and we love looking back on the fun we all had together as children.
My experience of having a sibling was definitely one of the driving factors in having a second baby.
However, I also know lots of people who were only children who loved it as chikdren and love it as adults and don’t feel they missed out at all.
There is no right answer.
Don’t have a second baby just for the sake of providing a sibling though unless that’s an important factor for you too. You have to want a baby for your own reasons, not just because you are thinking of your current child’s future.