Hi George,
It's not an unusual problem actually

It's impossible to put an exact cause on it without knowing you better, but probably its an aversion to success.
We all seek success because success leads us to what we really seek, which is validation and ultimately love. We seek love from others, the ultimate source of love however comes from within (this is just as true for women as men)
However, at some point in our lives each of us has been hurt. We've had love and validation from others, then we've had it removed, often suddenly and without warning. Ouch!
It's the times when our mothers have done this that cause the most scarring in relation to women...
So what happens when we are hurt? We put up boundaries. We say 'I'm never getting hurt again'....
In many of us (myself included) this has led to a fear of women, and a fear of success in dating, because if we get validation and love, and if we open up to that, we are making ourselves vulnerable.
So when a girl smiles at you, you feel vulnerable, and you get the fear. Thoughts occur such as
Does she mean it?
Is she being serious?
If she is serious, what can I do to make sure I never loose her?
By and large, these are programmed responses that were originally directed to our mothers pre 7yo, and are now being projected on to women.
What to do about it?
The most powerful way to deal with an insecurity is to tell the world about it. Not everyone will be understanding, but many people will be, and who wants people in their lives who aren't understanding anyway?
Insecurities are lies we tell to ourselves and the world. Things we try to hide about ourselves. Tell everyone, and boom!, no more insecurity. Just you, in truth, facing the world with real confidence.
So next time you feel nervous when a girl smiles at you, tell her. It won't get you laid in the short term but in the long term it will lead to real abundance, because pretty soon you won't feel nervous any more
Good luck!