This is true. New circles will come, some will go again.
The same thing happened to me in my mid to late twenties. By the time I was 30, most of my old social circles were settled/settling down. I'm still single and living the life I want nearly 9 years later. I've moved around a bit and lived in and frequented places where there are people to match my concurrent mood and outlook. It takes a bit of trial and error, but we get on fine.
Twenty-five to thirty-five is a hugely transitional decade in life. If you're not wanting to settle down, it's a good time to really proliferate success and worldly understanding for the future. I hang with some older guys in the pub now and then and a couple of them are borderline polymaths; insomuch as they are very knowledgeable and skilled in a number of disciplines - making money, music, art, cooking, crafts/DIY, tech, sports, whatever. You can tell that they have spent a good many hours, by themselves, honing their skills and knowledge. Really quite inspiring to see.
It's good to be good at things, especially at the moment when most people aspire very to little, beyond social media attention-seeking.