I am really crushing on a girl. i feel she will just hurt me. How do I stop having that defeatist attitude?

there's this girl i used to work with and i want to ask her to hangout with me. i went back there and was about to but the conversation was interrupted bec. she was @ work. i get so friggin nervous. it's like a mix of getting the air knocked out of you and erfulies. it took me a lot just to talk to her that time. we have talked to eachother in work but the pressure is so high because my feelings are so BUILT up to the point if she rejects me. i don't know if i will be able to be confident again. i mean i'm turning 23 in about 4 months. i never had a gf or even a date. girls are never the first to call me. i call them and sometimes they dont' even call. i had a girl tell me i can have HER and asked what we ARE and then we get into an argument and she says she HATES me and that she never called me. from then on i didn't really have full confidence to approach to girls. i talk to girls and if a guy talks to a girl and get's her all happy or whatever I feel so BAD and i feel like i'm not good enought o be with a DECENT girl. i have no FRIENDS and my FAMILY is concerned that because they see i don't have a gf or ever go out. my bro is 18 and has a gf now and has had one in the past.