This is purely anecdotal, but my DD is an only, and I am not lying to you, she has about 25 friends. I mean REAL friends. Friends she can rely/could rely on if she needed something, needed somewhere to stay, needed help with anything etc. I mean, she has us obviously, but if we can't help her, one of her two dozen friends will.
And, she has friends in London, Brighton, Manchester, Birmingham, Cornwall, Devon, North Wales, and Edinburgh. As well as half a dozen close pals near where she lives/workmates. She ALWAYS has somewhere to stay when she goes to these places.
She made these friends (who live in other towns) at uni, and at college, and when she took part in things at uni that involved several other unis. She left uni about 5 years ago, and still has contact with all the friends she made there.
I have never had as many friends in my lifetime as she has right now, (and has had for about a decade, as she started making lots of friends at college age.) She has a couple of friends at school, but it was when she left that she started making loads of friends.
tl;dr An ONLY does not have to be lonely. I have a brother, and have only ever had 3 or 4 friends really. Proper friends I mean. My BFF and me have known each other over 45 years.
I did have a few mum friends when DD was little, but they only lasted 3-5 years then we all moved on and didn't stay in touch. I am sorry you're finding it tough @Powersout I hope things improve. xx