Firstly, nobody is meant to have long-term friends or not. It's a situation determined by hundreds of factors; it's not meant to be anything; that implies some sort of reason or plan behind someone's existence and their interaction with acquaintances. It's something under the control of the individuals, albeit heavily influenced by factors such as distance, life-changes, family and especially as it pertains to those on the spectrum; social awkwardness and difficulties interacting with others.
I've only ever really had 1 friend at a time; going through phases of my life. But, I never can or want to put in the effort to see them - once I "partnered up", settled down, moved away and had kids, that takes up enough of my time, especially with full-time work added into the mix; the spare time I have left over I want for myself.
I currently have 1 friend, and he's been that for 5 years now. I classify him as a friend as opposed to an acquaintance or a colleague (he works at the same place as me) because he lives close, has very similar interests and opinions on those interests (taste in film, comedy, video games) and "gets" me. He never asks me to go out drinking, or to socialise with others, he's happy just coming over for a few hours a couple of evenings a month to watch a Movie and play some PlayStation. Incidentally, 75% of the time he initiates this. But, it makes me happy to have it this way - with my partner and children, 1 friend is enough for me. I dare say I'd be content with none; as interaction with people where conversation could switch to personal matters, opinions on things that are important to me does not make me happy, it puts me on edge and I don't like it.
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"You're entitled to your wrong opinion..."