@Ginghamsheep
Yes, it's perfectly possible to have a great time.
I'm an only child, both parents died young, don't have any other family left.
Don't have (& in fact can't have) kids. Never married.
What I do have is lots of friends and hobbies and all the freedom in the world to indulge them. And to spend time with my friends' children if I want (and, equally importantly, not when I don't want!)
Sometimes have a partner, but although I'd like to find someone for a long term life commitment, I'd definitely rather be single than settle.
I'm mid 40s, and I'm still making new friends at hobby groups often, trying new things, meeting new people... It's really very fun, and having recently ended a long term relationship, I'm actually enjoying myself more single, because I'm out and doing things more, whereas he wanted to stay in more, so I was compromising for the relationship.
I would suggest thinking about things you'd love to do, and then getting out to do them. And if you can't think of anything you'd love to do, find some things that you think ah, it might be fun, and go try them. If you don't like it, try something else until you find one that sticks.
Social dance lessons (swing, blues, salsa, tango etc) are a great way to meet people, feel alive and happy, and also get some light physical contact in, so can do a lot for your happiness if you're feeling a bit down or lonely.