She wants to f*ck around.
You're boyfriend material, not f*ckbuddy material. Simple.
She's not in the same place as you, so you need to move on from her. Even if you talked her round, you'd be worried about whether she is being faithful, and even if she is, you would be hung up on her 'past' with other guys,and the attention she gets, and her friendships with other guys, etc...