The problem is that by 35 you can't get by on novelty anymore because you've seen some version of everything there is to see.
The worst thing you can do is pine for the good old days. They aren't coming back. And they weren't that good anyway. Your best times are ahead if you can successfully adjust.
What worked for me was putting down roots. I resisted it mightily at first because I wanted to stay mentally 25 forever. Now I see that getting married and having a couple of kids was the right thing to do. It forced me to become more flexible, more deliberate, more focused and have more stamina to do hard things
I'm a loner by nature, so I can't imagine where I'd be if I hadn't settled down. I just know it wouldn't be as good.
Once you've got those roots down, life will lead you to what you should do next. Maybe being a full time parent, maybe learning to sail, maybe more successful entrepreneurship. Who knows...
EDIT: I don't mean to imply that everyone needs a family. What's important is to start living for others to some degree. Hedonism has famously bad diminishing returns.
Some people choose to do lots of volunteering or switch careers to social work. There's lots of options.