I'm also in my 30s so I get it. The only real advice I can give is that it just takes more work to maintain friends as we get older. I had to be the one reaching out rather than waiting for others to reach out to me.

The other thing is recognize where friendships came from. Most of it was just being physically near people. Sitting in the same classrooms day to day. If work doesn't create that space (or isn't good enough or you want to distance from work) you need something else that does the same thing. Join a club. Set up weekly beers with your friends. Or literally anything that puts you in the same physical space with the same people, routinely. A friend of mine gets together with his gamer friends once a year and they socialize off the game too.

The convenience of social media is also its weakness. The ease of connecting makes it just as easy to disconnect.

Real friendships require work. That's true of any relationship. I'll tell you my friends can be annoying and exhausting, but I love them and I'll gladly put up with their shit to keep them around. After all, who else is going to put up with my bullshit? lol