Disgusting is a pretty harsh adjective. I'd reserve it for domestic abuse or being mean to bunnies or the last two Shrek films.
Some people will find it ungentlemanly for you not to pay for the date. And that will undoubtedly include some women. Who may get angry at you. That's how it is. I personally don't think it's an issue at all, assuming you and your girlfriend are both on roughly equal footing financially.
It should be up to you and your girlfriend, anyway, not your pal. If your girlfriend is comfortable splitting the bill, wonderful, it's nowt to do with him. If she isn't, then you should examine the reason why, and work it out with her. Still nothing to do with him, but yeah.
"Darling, I want to pay for dinner because Johnny said I should."
Now, my personal ideals out of the way, I'd still pay for a date by default. Partially because, hey, I need all the help I can get, let's be honest with each other. And partially because I got brought up to think that way. Not necessarily by my parents but by, well, growing up with that sort of thing getting drilled into you, I guess. Same is probably true of your friend, OP.