I Like To Flirt But I Am Shy

I noticed I shut down when I'm with handsome/interesting men, and I don't WANT to shut down, it frustrates me. On internet....no problem. But in real life, when I meet a guy and he comes to close (literally and/or figurative) I get shy and can't say a word anymore.

I did have a bad relationship, my ex was manipulative and a cheat but I thought I was over it already and ready to move on. I don't know if it has something to do with him but could be.

I really want to move on, I don't want to shut down all the time....Normally I am fun and social, like to laugh and tell funny, crazy stories. I want to show them I am not always like this....Want to show the real me but can't....What do I do? Any experience with this anyone? Advice?