She has Multiple lovers, You have One,
she gets what she wants with no complaint from you, instead of having multiple lovers you derive your satisfaction out of one via compassion and support (Financial)
So tell her you'll come to level playing grounds since we are picking what we want to be mad about, that you both can only have one lover or she can have multiple and you have one with the added financial compassion you so enjoy giving. Bet that pisses her off! It's not like your giving your spouses money away or money that is dedicated to supporting the house or retirement accounts. I call it beer money redirected elsewhere.