Don't fulfill your purpose for yourself, do it for others. That's why it's called a purpose - it affects the world. Otherwise, it wouldn't really matter at all.
People need people. People are designed for other people. But, there’s still more to it.
Have you ever felt lonely? I definitely have. But the interesting thing is that loneliness doesn't necessarily mean you don't know anyone. Knowing people has close to nothing to do with being lonely, because you can know people and still be lonely. True loneliness occurs not when you don't know anyone, but when you don't feel valuable to anyone.
When you go against your purpose, or if you don't know what it is yet, everything starts to get blurry. But, you're still alive, right? You're still breathing, right? Yeah, you're alive. If you didn't have a purpose in life, then simply breathing would be sufficient. You have a purpose. Maybe not for yourself, but most likely for others.
Finding that purpose, if you're unsure what it is, is another thing. However, I suggest not worrying about it. Instead, think about how you can help others. Why should you care? Well, for one, there's people out there that need you. And another reason is that helping others helps you in return. So, you have a purpose in life, but it's main focus is not to make you feel good. (Although, that is one of the side effects.)