Tried meetups... Too much posturing and no vulnerability.
Tried online groups... Too digital.
Very curious to see how people handle that loneliness. It's terribly hard at times.
Online games changed my life when I was deep in/under the valley of startup desperation. I met people I could talk about non-work things. Or whom I could joke with about my job. That also helped, trying to see the funny side of the harsh life of a company founder from the outside.
That was four years ago. Company is doing better than ever these days, not particularly thanks to me. And I don't feel too lonely these days.
Another thing that worked for a friend of mine: writing fiction. He says his characters live in his mind, like he is the hardware running the world of his books, so he never feels alone. And he also gets to interact a lot with fellow writers in the real world. Fiction writers are a very different bunch than software developers, it seems, they are more concerned about people feelings and such.
Hard to force myself not to...
Watching sports helps but there's a huge high during it, then a massive low as soon as it ends...
Running a successful solo-business is a lonely route by definition. Few people are on a similar path, fewer still reach the summit. For me, thinking back to how much lonelier it felt to sit in a busy office knowing that there's got to be a different way, provides perspective.
Besides, perhaps loneliness is the cost of admission: a business is a path to wealth, freedom and possibly meaning. Happiness is not included.