What is going on here is that you are a chronic caretaker. Caretakers consciously think that they are giving in a selfless way, no strings attached. In reality, caretaking behavior is driven by all kinds of unconscious fantasies and expectations. Deep down, caretakers expect to finally be rewarded for all the good that they do. In other words, the caretaker takes care of others because he/she secretly wants to be taken care of.
In the end, all caretakers end up feeling used, empty, exhausted, and often angry. Why? Because free hand outs are most welcome. People are glad to take your giving and they will keep on taking as much as you give. Since you don't make any requests for yourself, the people on the receiving end think that you are happy to give and they continue to take. Meanwhile, you keep giving hoping that they are finally going to take the hint and start giving back to you. As you can see, this pattern leaves you sucked dry.
The moral of the story is this: If you want to live the life of a saint and martyr, then abandon all hope of rewards in this life. If you can make this shift, you will feel joyous, not depleted, in the giving. If, however, you want to receive rewards in this life, you need to live according the rules of the real world. In the real world, one doesn't give to people who don't give back, not unless they want to feel exhausted and drained. I think you get the idea.
In answer to your question what can you do about your predicament, as you can see, your question is larger than you realized. You have the short-term problem of what to do with your ex. and the larger question of how you are going to break free of this pattern so you don't find yourself in the same mess with another woman. Regarding the larger issue, begin observing your tendency to caretake. Each time you feel yourself on the verge of doing for someone else, ask yourself, 'Is there a string attached to my giving? How will I feel if I get nothing in return?' If you can honestly say that the giving will satisfy you in its own right, then give. If you sense that your giving is motivated by a need to get something for yourself, then be clear on what you want and ask for it directly.
The way to heal this pattern is through engaging in the above observation over and over again. In time, this technique will cause you to abandon your caretaking ways. As for this girl, first you need to decide that you are done depleting yourself. Then and only then can you tell her that you aren't willing to keep tending to her needs and rescuing her at your own expense. Then and only then can you can tell her to give you a call when she makes up her mind who she wants to be with.
It's time to take care of number one before your well is totally dry.