Not much to add that hasn't been said but, I am in a similar position, live alone, partner is long distance see each other every few weeks but going nowhere. I should end it, but if I do that I am just more alone aren't I?
I have a local pub that I go to. I know people in there and feel welcome.
I have friends in a different city but all at different stages in life.
I have never married or had children.
Me and my Mum are great but my Dad and I do not talk.
I am good company by all accounts, good fun, helpful, happy-I was a model until my late thirties, I know I am not hideous. I am a therapist and have two degrees-so it isn't that I am stupid either. No real reason that I've been left alone other than happenstance, and I am not autistic before anyone suggests that 
One thing I will say is I am not so sure regarding the several suggestions of 'get a dog'.
I have a dog. I adore her. She's great company, she makes people talk to me when we're out, she's beautiful and everyone wants to pet her. She's also huge-meaning if I do go out of an evening (to the pub or parents who live nearby) I am safe to do so.
BUT.
I can't just nip off to see friends, go to an event, go to a new hobby that's more than a few hours.
I can't take myself off overnight if someone does want to spend time together
I can't see my partner as often as I often do not have anyone to have her.
In short, dogs are fabulous but they can make your life even more isolated, in other ways-be careful if you're thinking of doing that.