You mean with Diaz? You have an interest in your sister, so does she. She essentially starts turning your LI into her pet if you don't cough up the money. You can choose to take part in this, yes, but it's going to happen regardless if you're not giving her bribes. Exact same thing as with the mother. Not having a dick does not change that.personally I wouldn't classify g/g as ntr either.
Not judging, I've done what there is of the pay/don't routes myself, but call a spade a spade.