Self reflection is always useful. Some of what is being described is social anxiety. Some of what is being described is developmental.
Broadly, I think there might be an issue of managing expectations. A great phrase I learnt on here "Friends for a reason, friends for a season, friends for life". I'd say in a ratio of 60:30:10.
A person is like a Rubik's cube, different people see different sides of you, you are constantly evolving, acting and reacting. Each friendship helps to build the whole you. Even bad friendships that go wrong.
You don't have to be like someone to like them. Other people are interesting specifically because they aren't like you.
I note several pp saying their hobbies are weird, or more intellectual than the mainstream, dare I suggest, isn't that a little presumptuous? Can I not like classical music and country, and teenage DD fave 1Direction. I enjoy Dr Who and Newsnight. I'm interested in medieval history and want to know what is the new Spring Summer fashion look. I have a keen interest in geopolitical matters, read The Economist, Private Eye and the showbiz section of the Daily Mail. I can also comment fluently on David Beckham's ahem, advertising.
I don't do geocaching, Game of Thrones, gaming or RPG but can see why someone might like my DH.
There is a myth perpetuated by social media that everyone else is living the dream. People present an edited version of what they want people to see. They aren't living the dream. Just as you aren't and I'm not. Social media is just a device to beat yourself up with. It's hundreds of other "friends" judging you. I don't need that, I can judge myself.
Some people stay where they were born and grew up as it gives them security, others leave because they are stultified by it, each choice is perfectly valid.
You don't need to be in a group to be legitimised, you need to be yourself. As pp said at different stages of life it is easier to make friends, at other not so easy, it doesn't mean you need to give up trying.
P.S. baby classes are the seventh ring of hell in my world. I was a refusenik. Just because this group of women gave birth at the same time as me, didn't mean I had to be like them bossy, self righteous, sanctimonious, claiming their baby slept through the night at 7 days and was talking at 4weeks.