Why would i be afraid doing this?

first off im gonna say in my life currently that i know of. there is only one thing that i fear. im deathly afraid of going out, dating otherwise being alone with a girl.when i say i fear nothing, im mean i dont know anything els that im afraid of. Guns, dogs, knives, speechess, ect...i know because i got a gun pulled on me (no im not like a gagangster) iv had people pull knives on me, iv been chased by a dog, and i wing every Speech had ever to give.during any one of these i ALWAYS kept calm and collective, hell i laugh halve the time someone trys a knife. its not that im shy. id say that im the life at any party! i mean im like an unstoppable force of charisma! but whenever i am alon with a girl i like, i always get so Quiet and scared out of my mind. How come its only when im alone with a girl? if im by a sum chicks with friends i flirt like hell! but when it come down to "want to go out sum time?" i just cant do it....why?