Being isolated from your tribe used to be a worse punishment than death. The greeks called that punishment ostracism. El mio Cid was the Spanish representative case.
In the US there is an epidemy of loneliness.
So, what to do? First recognise that this is a problem and do not dig deeper. Do not isolate yourself more. Do not play vdeogames, do not read books until you fix it.
My main advice is to stop thinking too much about yourself, think about others.
I was into religious(Cristian catholic) orgs and I helped old people(something I did not like), I helped poor people on the streets(liked it more) and I helped drug addicts and war refugees.
Helping drug addicts were a pain on the aßß, but once you make someone get out, he or she becomes a friend for life. It is like the friendships that are done in fighters of a war. Once you have put your life on the hands of someone else and trusted someone else so much, nothing can break that friendship.
If you think about that in a meta way, I was helping people that were marginalised, that were alone, and in the process I could not be alone. I did it in a religious group(a tribe in itself)
Thanks to this experience I can make friends very fast in a new place, something few adults know how to do.
If you are going to read, read a book called "How to influence people and make friends", but do not read the new book that is a badly revised book by the incompetent descendants of the writer, read the old original book.
But reading books is not going to help because you need action first, not reflection, and action is going to be painful for a while, and you have to endure the pain until it becomes easy. The best advise is to get out there, try hard, fail spectacularly and only then read the book.
Stop thinking about yourself, me, me and me. We are not wired to work for us alone. We are worked for working for others: Our tribe, our children, our family.
Instead of not trying to be alone, focusing on yourself (me, me and me) start thinking on helping other people that are alone. Start thinking on creating your own tribe or joining a new tribe. It can be a maker space, a group for hiking or helping or teaching kids.
Looking back on the last two years and auditing what worked, I would say routine and lingering were the most important thing.
Trying new things is mentally draining and labor intensive, this is a fact of life for many. What worked for me was finding something I enjoyed (exercise classes) and doing it consistently multiple times a week at the same place for months. With repetition, it's very easy to make new friends. Complaining about one exercise one week turns into making comments about the music the next, and all of a sudden you're getting coffee with friends.
At the start it was very difficult, and I was very bad, but now I'm part of a community and have many close friends. Its a hour per day most days of the week. It's also a jumping off point for everything else social. It provides purpose and self-confidence. Which are prerequisites for everything else meaningful in life.