A sibling can be a very positive thing when having this illness. You can't have enough loved ones and support, especially if suffering from a mental illness.

I have a brother. He's much older than me. When I was very young, I would beg my mom for a baby sister. My brother was very cruel and abusive. We went through some good times together, but I mostly remember just pain and disfunction and some pretty bad PTSD type symptoms which still linger and probably always will. I wish things were different, but to make them different, I'd have to be able to change the past.

So I guess my point it, a sibling might be amazing and supportive, or they could be triggering and toxic.

All hope is not lost. It's possible to find a friend who also doesn't have siblings... And develop a lifelong platonic bond. I bet there are a ton of people who would love to be friends with you and would find it cool to be SUPER BFF's.