I, too, wonder how one makes friends when one is an adult.
We moved to where we currently live 15 years ago. My daughter is now in the 7th grade. People told me we'd meet lots of parents while she's in school and would be able to form friendships. Hasn't happened. Not for any trying on my part. It just seems they already have their friends and don't need any more.
We live in a little rural sub division. When we moved in, all of our neighbors had old children while we had a baby. Now that our daughter is 13, the neighbors are either childless (children grown and gone) or new families have moved in with very young children. Both neighbors on either side of us are alcoholics. There is no getting together and having morning coffee klatches. The neighborhood just isn't a very friendly one.
We belong to a church, but I've never felt comfortable with spending all of my time at church just to make "friends." I have some parents through my daughter's Confirmation class whom I like and have a great time visiting with, but not to the point where we do anything outside of church.
I am also in the unusual position in that I work at home as a freelancer and can make/keep my own hours. So I am open to doing something during the day or catch lunch with a friend. Except for those who work, they usually run errands during their lunch hour and aren't interested in getting together for lunch. Most of the people/friends I have to get together with during the work day are friends of mine who are retired. Seriously. Don't laugh. They love to be able to get together and do something. While I love them and their friendship, I would also like to be able to get together with others my own age once in a while.
I've tried joining different groups that I'm interested in, but unless I'm 100% invested and continuously am always volunteering or doing something, any and all "friends" sort of drop away over time, even though I make an effort to remain in contact and try to maintain a relationship.
It's as if all friendships these days are situational friendships. No one wants to or is interested in commiting to a long-time friendship. It appears to me as if everyone is so busy running around that no one slows down long enough to do something as simple as creating a friendship. AND you have to have time when the other person has time (lots of people have dumped me because I couldn't fit my life into their schedule) AND lots of money so that you can go out shopping or eating or to some other "thing" where you hang out together. When did it become uncool to go to each others house and hang out and visit? Since I only bring in a little income and we live off my husband's, I don't have oodles and oodles of money to spend. So that gets me checked off the "call list."
We live in a big-10 college town, and I've noticed that it's harder to get to know people because people are always moving in and out. I'm slowly meeting people who are from the area, but again, making friends is a slow-moving process.
I'm 45 years old and have pondered the friendship question until I'm blue in the face. I am an extrovert working an introvert job. I guess over the years I've just gotten used to the fact that I either spend my time alone or with my husband or my daughter.
I might be PMSing at the moment too. Sorry my post wasn't more happy and enlightening, but I can feel your pain because it's my own as well. I also have a hard time finding people who share my thoughts and ideas and beliefs, so that makes it doubly hard. Although lately I've been finding groups of people who do share my thoughts, ideas, and beliefs, so I'm hestiantly excited that I will find a friend or two out of these new ventures.
Just keep doing those things you like to do and continue being you. You will attract others who like you and your beliefs and, most of all, who you are. After all, what you really want is an authentic friendship. Those take a lot longer to find and nurture.