It's all about common interest really and how much social intelligence you have.
If flirting doesn't come natural to you. Or if you have trouble pulling crap out of your head to spew from your mouth so others can digest it and find things to relate to. I mean the list could go on, but there is a key set of requirements to acquire a "group" of friends.
Finding a "best" friend also has a lot to do with synchronicity and being in an environment with at least a hundred or so different people on a daily basis.
If I recall correctly in high school, I had 2 best friends. The first one lasted for about one year, then I went on to the next one. It was just a matter of bumping into somebody. However I was in, keyword here, "high school". Then you can MAYBE go on to something like college and have an equal base of people to work with.
Once you get beyond all that crap basically you'll find such opportunities just don't exist anymore. You get older, people find their place in life.
Established social groups are really nothing more than people who are taking comfort in each other. ganging up as a group to fight the same feeling your talking about. So that with-in their social group they are safe from that feeling. So it's very difficult depending on the type of person you are to "get into" a group that you may only be able to observe from the outside.
You have to have a "reason" or better a "justification" for invading their safety. In much the same way you might want to bear gifts to a neighboring tribe to improve good relations with them.
So you have to think in terms of, what do I have that this group doesn't have? Well the group has people already obviously or it wouldn't be a group.
I think a better approach would be to get involved in group activities. It can seem like a daunting task at first, but there are tons of em out their if you search hard enough. That way your not really invading anyone's security. Your putting yourself in a position to be sought out because people are seeking to create and form social bonds, rather than exclude people who are different out of fears, social anxieties, and differences.
There's church if your churchy, voulunteer programs, the gym,... i dunno... tons of honeysuckle...
Personally for me... I have 1 friend left over from highschool who I never see anymore, but talk to occasionally. A small hand full of friends I met from my last most secure job I've held. And I made a bunch of aquaintances from my last job, but none of them gave enough of a honeysuckle to stick around as true friends.
I haven't had physical contact with what I'd call a friend in over a year now and that's nothing new to me. Half the time I find the people I do interact with just make me feel shittier than I did when I was alone anyway.
***you might not realize you are a difficult person to approach*** this is something I'm learning about myself. I'm always very deeply entrenched in thought, even in public... and I think it makes me a difficult person to strike up casual conversation with. People feel like they are interrupting some terribly important conversation I'm having with myself, lol... which might not be far from the truth.
Don't resent people, though, people are stupid. That's fact. Persons, however, if your lucky enough to really get to know a person can be quite insightful.
I remember just the other day walking around on campus looking at people just sitting around and having conversations. All the while wishing I could have some one to just sit down with and shoot the breeze with, but then I remember (your dead inside and have lived most of your life already... you'd probably be doing that if you actually had anything to say anymore,
)... heh...
Don't be resentful though, I'm thankful for even the few minutes I get to talk to people over a cigarette.
