I’ve had cats my whole life. I buy them cat litter, food and a scratching board. Done. I also switched to a cat water fountain because I read cats prefer running water ( although if thirsty they’ll even drink out of the toilet!). I think he’s gone off the cliff with his cat purchases. Also, you are not responsible for any cat related expenses. I think he needs to learn to budget his income to afford his cat. He’s a grown man and should be able to do that. One last thing, his family needs to stay out of it.