I've met more than just a couple of people who did not seem to have friends after they graduated from college. I talked to a middle-aged woman once and she told me that after college, you'll get married and that'll be that. And she says that she doesn't even talk to her best friend any more.
I think it's more - once you have children, you stop having friends.
I have no friends outside of work, it's pathetic. I never talk to any of my college friends anymore, I have no idea what they're doing. And when you go out with work friends your job dominates the conversation so it's like you can never escape it.
Do you stop hving friends after college? That's up to you.
If you make having friends a priority, it seems like it wouldn't be that hard to find them. Seek out people who share your interests, the internet is a great tool to find them.