he took full advantage of your weakness on the flop. it does not matter if he had a set here or 7-2 off. you showed weakness by raising pre and checking the flop, so he figures he will follow what you are doing then throws out a nice bet you cant call!! so i think you win this by betting 70%+ of the pot on the flop and two things will happen he snap folds and you win a nice little pot or he re raises you.