How to help out this shy guy?

im usually really outgoing and funny, im friends with a lot of people and im friends with a girl i really like. sure i can still be outgoing and stuff with her, we're real close friends and i dont know if she likes me, all i know is that i do. and i dont know how to bring it up, im scared about ruining our friendship. and it doesnt matter about who i ask, whenever i get to the point to ask a girl out i clam up, i cant seem to do it. i've only had 5 relationships and they were the ones to ask me out. i never could manage to do it myself