Women do not operate with a code of honor. They do not feel obligated to repay your sacrifices with loyalty. When you spend on her, provide for her, and go out of your way for her, she does not see it as something she must repay. She sees it as your role, your responsibility.
She will take everything you give and still leave when she finds someone who offers more. She will not remember the sacrifices you made, she will only remember that you are not giving enough now.
So do not expect her to be loyal because you gave. Protect yourself.