I think grown ups, for the most part, suck at friendship and we often have no good role models for it. When I was growing up, no one modeled successful adult friendship for me and I'm only just now (age 42 1/2) learning how to become and stay friends with women. It's the "staying friends" part that's the challenge. Even after I learned how to make friends with women, I used to give up on them at the slightest disagreement and for most of my life I've had no friendships that were older than a few years. I didn't like it, but I didn't know what to do about it. By hammering away at this friendship problem and not giving up, I have finally started to learn the following:
1. Not every friend has to be fascinating, intelligent, hilarious, attractive and have amazing connections. I've learned not to cut people off because they don't have my same sense of humor and my same interests, etc. because often those people have other gifts I haven't noticed yet. Maybe they give amazing legal advice or have in-laws just like mine and can relate or have insight into my job situation. You also never know who's going to turn out to be the friend who stands by you in your worst times. It's often not who you expect.
2. Even if someone pisses me off and is clearly the most selfish person I know, those aren't reasons to decide she's not my friend anymore. It shocked me the first time it happened, but I have actually worked it out with a friend I was in total disagreement with and today we're still friends. Believe it or not, people are often approachable and open to talking it out. If someone really values me as a friend, they'll want a chance to adjust behavior that bothers me or at least listen to my viewpoint. It takes bravery, but after a lifetime of fear, I've finally started giving people a chance to work on a friendship instead of deciding that a bump in the road means it's never going to work.
3. If I stop being friends with everyone who displays poor judgement or co-dependent behavior or bigotry or general assholery, I will have no friends. This doesn't mean putting up with a bunch of jerks who mistreat me, but it does mean allowing people to be human and maybe talking with them about it. Definitely I want to give friends as many chances as I'd want them to give me (OH, yeah..).
4. It's important to have many friends because some WILL fall in love or move away or become serious jerks you have to cut loose or whatever and then you'll need your other friends to fill in the space they left. This is another reason I don't put too many expectations on every single one of my friends: if I can't get love and support from my closest, most bestest friends, I'll take love and support from my not-so-close friends. Love and support are that important.
5. Every woman I've ever talked to about this stuff has had a LOT to say. We women tend to be so afraid to raise the topic of friendship, but we all have the same fears and feelings of failure about it. And many of us have a similar level of loneliness.
I don't mean to sound like I know everything. I've learned all of this the hard way and I still get judgmental and impatient with people and I still fight loneliness all the time. But I think if you can stay in contact with people and not have this reaction when they make a mistake, "Oh, she's THAT kind of person. I can't be her friend anymore," then you can really build a social circle. When you do, stick with it because you never know who you'll meet through these kinds of social circles. Some of us actually are fascinating.