Aloha Kitty,
I would talk to him. On one hand he was being honest and it was a game you both agreed to play. I am not sure of your relationship but I gathere he did not say he currently has four subs. Therefore from the outside looking in it doesn't seem that your Dom is curently a 'monster' (if he ever was).
Don't get me wrong I understand your feelings but if you tell him how you feel and that you wish the security of being his only sub, he may well agree and be flattered you desire him so. He may say no but you will at least have give it a chance. Would you really prefer he had said nothing of this feeling he was unable to confide in you?
I keep my claws crossed all works out for the best for both of you.
Regards Dragon