Getting pushed away.

So I've[m18] been seeing this [F18] and I'm really into her. She's smart beautiful and fun to be around. The only problem is that she keeps acting like I'm predestined to hurt her. She says she's been hurt by other dudes and she's guarding against it.
She brings it up way to often and it really kills the mood. It's like she's pushing me away and I have no idea what to do.