I've lived on my own for some years and I couldn't/wouldn't live with someone else now but I'm retired and 70 years old. I can understand though why someone younger would want a partner and not be on their own.
When I was married we had a very good life style: nice house, new car every couple of years, no money worries etc etc and I imagine someone like you might have looked at my life from the outside and though how lucky I was. I wasn't, I was lonely and thoroughly miserable.
Now I'm lucky. I have a decent income and I'm my own person and no one has the power to make me unhappy.
Stop thinking you can judge a book by it's cover. Yes, the people you know might have wonderfully happy lives but they might be, as I was, living a life of quiet desperation. Sometimes the grass isn't greener.
I realise that it's not the same as having someone to live with, someone who is there supporting you emotionally and sharing the financial burden, but if you're lonely get out and find some things to fill the lonely hours. Find things you enjoy and ways to meet other people.
I know it's hard when it's only you paying the bills. After my exh left I had to manage on a very depleted income with three DCs and financially it was very hard but the fact that he was no longer there making me miserable more than made up for it.