I identify so much with R36 and R52.
R36, I could have written your post a few years ago. I started therapy a couple of years ago in my 40s. I wish I had started 20 years ago. In getting a therapist, I got lucky. I called a group practice nearby and they picked someone out for me. It was a very young, social work graduate, working towards licensure. I think younger people are less judgmental, and they're enthusiastic to make a difference.
Like R52, I'm a workaholic. My weekends were for resting, and that meant being alone. (Not that there were a lot of people clamoring to be be my friend anyway. I'm an unattractive woman, and after years of bullying, my naturally introverted personality isn't that sparkling either.)
My other problem was my mother. She's an energy vampire with a deep need to talk (to me) about her problems. Because of her psychotic disorder, she had a lot of problems, most of which were not even real. She would call me almost daily and drone on for up to an hour or two at a time. Same (imagined) topics, over and over again. When I hung up, I would be drained, and I didn't have any energy to talk to anyone else. This started when I turned 21 years old.
In summary, since childhood, my problems are: intensely introverted personality, social anxiety since toddlerhood, years of bullying during adolescence for being "ugly", being gay (that's a trauma), and my mother's dependence on me to be her emotional support person. That combination of things killed my self esteem and made me feel like an alien observer of the human race.
In therapy, hopefully you will learn something about "cognitive distortions". (Google it now.) They continue to affect your self esteem. for years. Go to therapy RIGHT NOW, identify and fight them now, before they grow any bigger.
On Reddit, there is a a group called r/foreveralonewomen that's filled with people in the same predicament as you. You're far from alone. Warning: the self-hate there can be toxic.