I'm not going to cook differently for my girlfriend
Do you just not want to, or what?
She eats way too much, and the stuff she wants me to cook is way out of my league as someone who only cooks when he needs to.
It's your right to say 'no' about cooking her food. It may upset her, though.
That's fine, since I didn't think she liked my cooking anyway.
Well, I hope that she understands. You will need that to avoid a fight with her, I think.