How do I let go of my social fear?

I have this fear of interacting with people in public. When I was in high school I honestly couldn’t talk to people in public with out seemingly mentally shutting myself down and having to escape and go somewhere alone. Since then I have gotten so much better. I can go out with my friends and have a good time. I do still have this problem with talking to girls though, I want so badly to have a relationship but I shut down every time I try. I think I maybe deeply afraid of rejection and it shuts me down to a point where I can even talk and then walk away/escape.

Any advice or help to get over this fear of social interaction/rejection? its kind of reducing the quality of my life.