If he's your Master surely he must be allowed to see who he likes. Even if that causes you to curl up inside. If he is your partner as well then that may be different, it depends how you and he see your D/s relationship. My previous Dominant often used to talk to others and tease me with it. To be honest, I got very jealous to the point that I had it out with her. It was all part of the learning process for me. But if in doubt, talk to him. Good luck.