To start, I'm okay being alone, but I sometimes try to take an objective look at myself. I try to understand how I think and do things the way I do.
If my brother didn't live with me. I would probably live alone. I work from home and have infrequent meetings, outside of that I would probably have almost no interaction aside from the people I see doing my weekly grocery shopping. I have probably 2 or 3 people I could call a friend, and a few acquaintances, and all of them are previous coworkers. My interactions with them are generally constrained to discord chat. This is simply setting the stage, lets continue to set the stage for how did I get here?
If I'm being critical, I don't know that I have ever had many/any friends. In grade school, I had neighbors who's houses I would go over to, but I don't think they ever came over to mine. I was a member of many clubs, but I didn't really talk to any members outside of the club itself. After starting college, I think I might have kept in contact with one person from high school, but that was only once or twice. I haven't talked to anybody from then for over 10 years.
Surely people from college, right? Well, again I was in the marching band and lived on campus, certainly many friends from there. Everybody in band has a friend right? Other than attending alumni events, and some volunteering, I don't talk to any of them either.
So what does this all mean? Well I think I can say I can be alone in a room full of people. I can go to a meetup, after working though the anxiety that would keep me from attending, and leave after barely talking to anybody. I have anxiety that keeps me from going to events where other people would be, and if I do go, I have no idea how to interact. In general I would say I don't really know how to start a conversation with others outside of a professional setting. I can respond in a conversation, but leading is out of the question. I'm bad enough at reading people in person, online I'm even worse. It takes effort for me to only say "fine, you?" instead of a full explanation in response to someone I know saying "hi, how's it going" as a greeting.
I used to say I was an introvert, but I don't even know if that's true. I'd much rather do things with someone else than just alone, I just don't have anyone to do it with. I just don't want to be in a group of people having fun, and not knowing how to even start a conversation. Anyway, yep I'm lonely and usually okay with it.
For reading the above, here's a silly music video with lots of cartoon violence (including cartoon death) https://www.youtube.com/watch?v=X-atRsitNsY Song is let your love flow by the Bellamy Brother and animation is by Tirrelous
It's also just hard to make/keep friends in the digital age. My only advice would be to make active effort in building and keeping relationships, and not to be passive in hoping people will stay around. I'm often guilty of zoning out for a few months and forgetting a lot of my friends exist. Social anxiety sucks.