Why do I stay with her?

If you continue this relationship you will not be happy in the long run. You will someday will have the straw in the camel's back and it will get messy. If you're a self-confident person, uming has a strong personality, then maybe you can rationalize your relationship with her and be able to move on. If she has some understanding of how this is what you're pion is then it shouldn't be a problem. She should 100% support you.