"Know thyself" - Socrates
If you cannot live with yourself, what makes you think you are ready to live with others?
Most people don't want to be alone because it means they have to face themselves. I spent 5 years alone to get there. Not many people are willing to know themselves so deeply because they are terrified of admitting who they are to themselves. Yes, it's ugly at times when you tear down the illusion you have for yourself. But it's beautiful too when you find something to admire. And better still when you learn how to confront those illusions.
For me, there is nothing inherently wrong or bad about being alone. I think too many use others as a crutch to avoid themselves. I go out to eat alone. I go to movies and concerts alone. And it doesn't bother me at all because I can treat myself right. I have become selective about who I allow into my life and how I allow them to treat me. This isn't lonely, it's self care and more folks should embrace it. If you regularly treat yourself to your fave meal, book, tea, or experience even alone, then you learn that others being around more often detract from your experience.
I feel less lonely now than in 25 years of marriage. I could of course feel the other way, but by learning myself, I know I don't need others to feel valid. I feel happier and healthier with fewer high quality relationships and treating myself well in between.