Hi Minerva I totally get what you're saying. I'm an introvert and despite being out a very long time it is hard to build friendships from scratch when you lose all your friends and most of your relatives.
Most people at work have large extended families and still keep in touch with school and college friends. I don't have any of that because of course I wasn't allowed to have friends at school or go to college although I got a degree after leaving. Well done doing that yourself and getting your masters and then a good job. Brilliant!
I have joined a local group I found on Meetup.com and also a book group. We do meals out, Xmas drinks, pub quizzes etc. I've realised that the people who join, many have been divorced or their partners have died or they're new to the area so people find themselves isolated for different reasons apart from cults.
Also at work events I did sometimes feel odd especially at Xmas because I didn't know what to expect. Just have a glass of wine and try and join in. You might get a taste for it 😀