Detailed question looking for adult responses?

Its a complicated situation because on one side if you continue to just be there everytime she finds her way back your always going to be her plan B...like oh if it doesnt work out with so and so I can always go back to whatever your name is. But at the same time you dont want to give up on someone you care for. No one expects you to. But you do need to make it clear that you are investing yourself in this relationship and if everytime you get close she wants to pull away and end up hurting you its not fair to you so she needs to decide...not as an ultimatum but because it isnt fair to you. Also, she might not be exactly open to it but maybe she should go to therapy or something to try and make sense or why she has issues committing even to a person that she cares about. It would make your relationship a whole lot easier because you cant fix a problem if you dont know the cause of it.