I think you have to accept that loneliness is part of the package, unless you take specific efforts to counter it.
Being a founder is inherently isolating because you probably work extreme hours, and are not a peer relationship with anyone else in the company apart from perhaps others in the C-suite due to the inherent power differential.
You say you can't quit, but I think you should rephrase that. You essentially acknowledge this yourself: you can quit, but doing so would have consequences. Turn that into an equation, and verbalize it / write it down. I'm not sure why, but it feels different than just thinking about it. On one side you have $X million dollars, and on the other side you have the costs associated with it: burnout, unhappiness, but also providing employment to others (not all negatives, fill out the equation as per your perspective)
Then break that down a little further: you might be able to address burnout (give yourself some odds, and a cost in time/energy for that attempt), quantify exactly how unhappy you are and how that's trending, and then acknowledge that regardless of how your company performs, your employees will (very likely) find other jobs. Most will do it anyway even if your company survives.
Your sides of the equation might look a little different, but the basic approach is to just divide it into an equation and start pulling apart the components. If you're unhappy but it's getting better, perhaps that's not so bad. If you're unhappy and are on the verge of suicide, it's worth thinking strongly about if it's time to move on.
From my understanding the general advice on burnout is that you should expect it to take months to recover from, but individual cases vary greatly.
On the subject of loneliness, I'd try focusing on non-professional relationships. There's too much power-play in professional relationships, even when there's no current exchange of value.
Perhaps most importantly, in your personal relationships, don't say what you do or be a bit vague. Be extremely modest. "I'm a founder of a company" becomes "I work at a startup" or "I'm in XYZ industry". Try to find people who enjoy being around you for your personality, not what you are.
Personally I went the other way and found hobbies I can do individually. There's a reason so many people in software turn to woodworking afterwards. There's a sense of progression, zero bureaucracy, and it feels like artisanship.