I want a girl I can have, but at the same time, can't, what do I do?

Well if you really want to know what she's thinking you have to talk to her about this. If you're sure she likes you back that shouldnt be a big issue. She may also have some of the same insecurities you do, and that can help to make you feel better about your insecurities. If she doesnt have the same insecurities, it will still help her to know where your feelings lie.