Keep your friends close, keep your enemies closer.
I think both Gold and Regina are using each other and neither one has a scrap of loyalty toward the other. Mr. Gold is definitely pursuing his own agenda, but since Emma’s goal of defeating Regina coincides with his goals, he will “help” her, for his own purposes. I agree with belleoftheball that Gold’s ultimate goals and nature will be murky until the end of the series, and he will flip when we expect him to flop and vice versa. Which of course makes for an awesome character IMHO.