Name changed but a regular.
You are not alone, it is nothing you have done and I suspect there will be nothing you can do to change it.
It’s because you are single and many of us experience it.
I have been alone now for many years after losing my DH in an accident.
My first shock was being left out of social arrangements which we were always included in as a couple. Just at the time when I needed my friendships the most they dissolved in front of my eyes.
I spent a long time questioning what I had done wrong or whether I was just unlikeable. Two years ago one of those ‘friends’, newly widowed herself, told me that it was nothing personal it was just awkward having a spare female in the group. The balanced dynamic had been disturbed.
It is the same in the small village where I live now. Lots of couple events, but very few I am invited too.
However, it really doesn’t bother me anymore. I have a lot of friends, all my choice and all related to activities that I really enjoy. The majority of them are single too.
And loveliest of all is the fact that when I am with them, I don’t have to smile sweetly and listen to someone’s boring partner, sit awkwardly watching a couple bicker all evening or even worse end up in an ‘agony art’ role.
You ask what you should do and I would suggest finding some groups focused on your real interests and nurture new friendships that way. There are a lot of single people out there, many also feeling lonely and happy to meet like minded friends.