Most Helpful Guy
I think it's okay, but I also think you should talk to him about it FIRST, and at a time and place where you have a chance to have a conversation. Do NOT wait until a waiter hands him a check to have the conversation, or he'll be way too pressured to pay no matter what, and then he'll be angry and resentful for being put in an awkward situation. Resolve the issue ahead of time, and everything will be fine.
I'm sure he'll still work hard and do nice things for you, but if you're an order of magnitude better off financially, you are correct that you can't expect him to keep up with that.