I am speaking to you as a friend...
You have to let her go...NC for a VERY long time. I am sure she is a nice person and fun to be around, but she is using you and does not love you. Are you really going to go down this road with her a 3rd time? She is not confused...she knows that she doesn't want you as a life partner, but she is too weak to admit to you or herself. From the outside she seems like a cold bitch parading with other men in front of you. How could you have any respect for a person like that? She doesn't even respect your love you have for her. She hurts you over and over again and you let this happen.
My advice is to try and find yourself. Don't sleep with anyone else or hang out with any other women as distractions b/c that will only back fire. Do not try and fill the hole and pain with drugs and alcohol b/c in reality that will only dig you deeper into despair. Find yourself and find what makes you happy. Love yourself and stop blaming yourself for not being what she wants. It's not about you. Stop subjecting yourself to endless rejection form this girl. She is short and a bit chubby anyway...