Pretty hard to avoid partying in certain contexts (a lot of people party in college, for instance). On labeling yourself "a party girl" or not, it's more a matter of degree. You're don't sound like what I'd normally think of as a "party girl," but depending on how zero tolerance the guy is for having a girlfriend who drinks / goes to bars AT ALL a little bit can still be enough (and if he's spent much time in the nightclub environment - which it sounds like he has - he's probably going to be pretty paranoid. You see all kinds of "that would NEVER happen" things happen all the time in clubs).
I wouldn't, say, call him up and tell him, "I've decided to not go to nightclubs since it's what you want!" because that's going to sound a.) like you're chasing him (and he'll lose some interest in you) and b.) like you're trying to mold yourself to his standards which, if he has any reasonable experience with women, he'll know never takes in the long-term… eventually people revert back to doing what they want to do.
On the same hand, I've had a girl who used to party try to get me back in part by saying, "You know, I realized partying is a waste of time and…" and it just sounded contrived and unbelievable to me (and, sure enough, we didn't get back together and a little while later she was partying again). So I wouldn't go that route either… it's both sneaky and obvious; not a good combination.
Probably the best move is to get him to meet up with you for lunch (or something neutral - not at nighttime, probably), and tell him that you were really annoyed at his objections before, but just had a long conversation with a friend's boyfriend who used to club a lot and he explained how even some going out and drinking introduces a lot of randomness and bad chance for things you'd normally think would never happen to happen. Then say, "Anyway, I don't want to break up with you over something stupid that you're actually probably right about," and he will most likely gleam with pride over finally being right with a woman over something, will realize you're completely brilliant for seeing things his way, and you'll probably have your boyfriend back.