I want to make my girlfriend split the bills
Why do you want to split the bills with your gf?
She spends more than I do.
That sounds like a pretty good reason! If she's spending so much, she should be splitting the costs with you. It's only fair that partners go half and half on paying the bills.
I agree, she better agree with me.
I hope so too, I'm sure she will see that it's a good plan too.