I can sympathise, being an only child of an only child, although my mother had siblings. They all lived hundreds of miles away so I've no cousins nearby and all aunties and uncles have now passed on. So basically it's just me, two children and three grandchildren. Thankfully one granddaughter lives nearby and I see her and her mum quite often. But like you, I often wonder what it would be like to have siblings and I'm pretty sure I would have treasured them.
I have done stacks of family history research and I think that is me trying to build a family for myself. Maybe you should try it. You will find you have a large family, even if they are all deceased. I have forged close connections with relatives who are researching my ancestors, maybe 3rd cousins. When you exchange photos and information you can get quite close to your ancestors' lives and almost feel like you know them.