The next time he complains about a light being left on you can reply that it sure doesn't cost as much as a hotel room.
My H spent lots on OW, too. Immediately after I found out about the A, I averaged all the extra cash he took out using our debit card, and what I saw on his credit card (before he started hiding the statements) and it was a few hundred dollars a month. A couple of months later I treated my sisters to a night out and he complained. I told him that the $100 I spent that night was nothing compared to what he had spent with her. He shut up.
You mentioned the constant reminders from him that he is in love with OW? Does he tell you this to your face?