My wife finds it necessary to explain heself if asked to go to play a sport.?

When my wife is asked to play a game of tennis with a genetleman whith who she had a premaritual relationship. She finds it necessary to give an explination and he ask why. Am I over reacting in insiting that her answer be No wothout explinaion. We have decideded that she needs to stop ociating with this person but she finds it necessary to explain why she cannot play badminton with hm.