Mistress Morrigan wanted to control her husband by making him wear a chastity device but he did not know that. He thought that she was trying to be naughty and she led him on to believe that. When he was done wearing it, she told him that she was now in charge of what he did with his dick. He could not believe it and knew he was cornered as she had the key to the device.
Mistress Morrigan was about to leave for a long a journey abroad and she was worried about her husband's chastity. She wanted to make sure that he was chaste so she tested him with someone else and when she saw some vulnerabilities, she knew she had to do something about it. That is why she opted to make him wear a chastity device which only she had the key to.