I'm scared to be alone in public, because I am so vulnerable.
Why do you feel vulnerable in public?
Because I always get insulted by others whenever I let my guard down.
Most people you encounter in public are just living their own lives, and won't think anything bad about you.  However, if you are worried about being alone, you could always find a few friends who can go places with you.
I don't like the idea of having to depend on other people for my safety.
In a way we all depend on others for safety. If you're uncomfortable being alone in public why not get some friends to share your time with?