How do you know when someone is your friend?

First, I have to say that I'm _not_ some teenager who's just experiencing difficult relationships and groups for the first time.

I'm actually a guy in my late 20s and partly a geek - I love computer games, reading, history, martial arts and archery. I'm certainly not shy, in fact I'm often outspoken and direct in how I communicate. I've never been massively perceptive of certain social behaviour, I prefer to do my own thing, but I consider myself friendly and generally well-liked by the people I meet.

Yet after recent experiences I feel that I'm struggling to understand how friendship works and how it 'officially' begins. And I know that seems crazy considering I have nearly three decades of experience, yet there seem to be so many unwritten rules and secret nuances, no one ever comes out and says "We're friends now" so how are you supposed to know?

How do you know when someone is more than an acquaintance or colleague or person you just occasionally hang out with or a mutual friend?

Over the years I've met people through college, university and different jobs. I give each of those people I meet one chance no matter how they look or how first impressions go, then instinctively I treat them as a friend. Yet the vast majority of those people don't really seem to make an effort in socialising or staying in touch after we split and go our separate ways.

People at one of the last places I worked (a large computer games developer) felt especially ridiculous. People in one group barely spoke to me after I got a position in another department in the company, including at least two people who I socialised several times with outside of work.

Then in the other department I was a 'go to guy' for a lot of people so I got to talk to and (so I thought) befriend all sorts but few wanted to hang out. Then there was one group of people I was with who would always meet up on a Friday down the pub, yet once a certain guy left (the one who would always organise getting people out) I found the others split into other groups and didn't invite me for anything. I felt offended when I heard or discovered them doing stuff without me, yet maybe that was fine for them to do so since we weren't (I realised) actual friends.

So how does that work?

Did my opinion on certain things offend them? How could it not be accepted? (And for the record I don’t consider myself an extremist in any field) Or if I made a mistake then how could I possibly make amends if I wasn’t told about it? Or were these people cowards, afraid to speak to me about a problem? I can’t do anything about it otherwise. Letting someone blunder through life instead of pointing out a problem, fearful that they will take offense, is surely much more atrocious in terms of behaviour.

Now it's been just over a year since I left and hardly anyone stays in touch bar two guys who I was definitely friends with. I have plenty of people on Facebook but, hey, that's just Facebook and not everyone on there is necessarily your friend.

So I'm left thinking: is friendship meaningless? For most people is it just 'mutual convenience' for a set amount of time?

I try to think that I shouldn't be ashamed of who I am, that I act rationally but I can't get over it. Am I blind?

Humans are weird.