15 years old and fed up with being seen as spoilt

I’m 15 years old and all my life I have hated being an only child. I only had time to skim through a couple of your stories in the research section but the first two I read definitely stood out to me. People always think I’m spoiled, but it’s not true at all and I often envy other people with siblings. I think one time I was at the grocery store and I saw these two siblings fighting over something. It was so cute how the little girl admired her brother so much and wanted to be just like him but at the same time was so mad at him for pushing her. The next time I looked over she was holding his hand and he was pushing her away out of “embarrassment”. I think I almost started crying right there and I am not a very emotional person. I knew I would never have that bond with anyone. I’ve always been a bit of a loner, but at the same time I have lots of friends. I noticed that one of my friends during lunch will always ask “someone come in line with me, I don’t want to go by myself” and I don’t understand it at all. A lot of times I prefer to be by myself and I hate me for that. It gave me social problems when I was younger because I didn’t know how to interact well with other people. But I’ve sort of figured it out now. People always call me spoiled and I want to punch every single one of them for saying it because I’m not.
As an only child, I spend WAY too much time alone with my parents and it’s caused some serious problems with our relationship now because I’m so tired of them. And then I get this thought, what happens when they die? Friends fade, but family is forever. That’s what they say right? Well what about when your family dies? Sure I have uncles and aunts and cousins, but sadly I don’t see any of them on enough of a regular basis to be close. If they are gone, and I’m still not married, I’ll have no one! No one in the world I can count on. But sadly, once again, that doesn’t even scare me that much because I’m so used to being alone. I’m so independent, I don’t need anyone. I’ve always figured out a way to deal with things on my own and I’ve always been very smart. I’m a very outgoing person and high achiever, always striving for the best, not accepting anything below that, but at the same time I am inverted certain ways. I feel like I’m missing something though, I don’t feel like my family is normal at all without that other sibling. I matured so much faster than all my other friends because I was always around adults or my parents because I had no other sibling. That made it difficult for me to get along with other people as well.
Anyway, sorry for the novel. All I know is I’m an only child, and I hate it and I hate that it’s so overlooked in our society.

Kimberley