I have direct although bitter experience of this. My Master is a sadist first and has learned through his relationship with me to express his sadism through being dominant. The relationship you had with your girlfriend and the things you did together sound just fine because it suited the two of you. But please don't present yourself to any sub as a Dominant only because of your experience so far with sadism. If you think you might now enjoy a D/s relationship then you have to present yourself as a new Dom and learn, learn, learn the new disciplines that that involves. To my mind a sub needs her Dominant to understand he must cherish and guide her, over and above any pain he wishes to inflict on her. The philosophies of Domination come first now and sadistic practices should be secondary to them. Good luck in your exploration.