I have found in the past that when adult only children speak out about their experiences that those who do have siblings are quick to dismiss us. We are quite often told that we are 'romanticising' sibling relationships and that we can't possibly understand what it is like to have siblings, yet somehow they can completely understand what it is like not to have them.
I would say that my life as an only child has been rather lonely. Probably more so now than when I was a child. I do have a couple of cousins, but we aren't close. They are close as siblings and they also have their own wider family, so I am not really needed, plus we are quite different people.
I worry a lot about being alone in life some day. Although that's partly my own fault for not having children of my own too. I met my partner later in life and he also has no siblings. I worry that if I did have a child of my own, I'd be bringing them into a very lonely family set up, and simply transferring the loneliness down a generation. It's like someone has to accept a somewhat lonely life, and morally, I think that person should be me.
If, when I die, I get the chance to come back again (not that I really believe in that kind of thing) I'd definitely ask to have a bigger family.
Of course I recognise that not all families get on, but it would have been nice to have had the chance. I think I am a kind, decent person and there is a good chance that any sibling I might have had would have had a similar personality. I can't see any reason why we wouldn't have got on. It would have been lovely to have had that bigger family network and the feeling of roots and security it provides. Someone to share memories of childhood with, someone to confide in and someone to share in the grief when my parents die. Maybe cousins for any children I might have had.
Of course I recognise that none of the above would have been guaranteed. However what has been guaranteed is that without siblings, none of it is possible.
A network of close family friends would probably have helped alleviate some of what I feel, but my parents are quiet, rather insular people, so that has never existed either sadly.