I'm going to make my ex pay the entire rent
Why do you want your ex to pay the entire rent?
I have spent a lot of money on her and she owes me
You are responsible for your own rent. Your ex is not responsible for your current bills and you should not expect anyone to pay your bills. If you do not pay for your own expenses you could get kicked out of your apartment.
But she owes me money! This isn't fair.
How does she owe you money? If she owes you a significant amount and she was supposed to pay you back then you can take her to court to get your money back, but other than that you have to pay your own rent.