This guy was always horny and he was always masturbating. That did not sit well with mistress Valentina and she wanted him to learn how to stop and he had to control his urges. He was too impulsive and that was what fueled his masturbation. So the mistress made him wear a chastity device so as to control him and get him to do what she wanted. He had no choice after he had worn it.
Mistress Valentina is hot and naughty. She was going away for a few days and she knew her man would be tempted to have sex as he had a high sex drive. So she had him wear a chastity device. The guy thought that she was being naughty but it turned out that she was tricking him to wear a chastity device whose key only she had and he would not be able to use his dick other than to pee.