From 18-28 life was sharing apartments with various friends just wiling our time away working easy jobs, rock climbing, video games, girls, etc. Then the looming pressure of "you are wasting your life!" drove us all into serious careers and relationships one by one.
Is it societal pressure that pushes us out of that life? It would be considered an "empty" existence, but being a part time bartender who just meanders around and spends time with friends/family until their time is up would be a weirdly buddhist lifestyle.
I have a much more relaxed feeling than I had 2~3 years ago. I am content, even happy, with the life choices I made. My family and I moved from Europe to South Africa, and while that has made the work side harder, the life side is so much better. Kids love it. They go to a much better school. We live outdoors most of the year. We hike. We sport. I took on surfing.
Like others have mentioned: reach out to those friends. Just a "Hi, how are you? I was just thinking about you and wanted to hear how you've been" can be the simple ice-breaker.
You're about at the half-way point for your life: what gives you joy? (playtime with the kids? learning a new hobby? ...?) do more of that! What gives you anxiety? (work? new boss?) figure out if you really need to spend time on that.
There are a thousand books about these things, but it's not really rocket science. Accept who you are. Accept who other people are. Make changes if you want.
It's never too late to call someone and tell them you appreciate them. It may not make you best friends again, but as long as you're both still breathing, it's never too late to reach out.
It makes me so sad to see people basically give up. Therapy is a great start. You only have one life. Get out there and live it!
And a flair for the dramatic!