Lots of wives would be okay with this! It isn’t a betrayal of trust, it’s not an open-ended arrangement with unknown scope and terrors, it’s plainly declared up front, it’s so infrequent that it has little to no risk of displacing the primary marriage relationship, it minimizes jealousy, it isn’t a side fling that could be stumbled across by accident in the everyday by the wife, it’s a controlled outlet for long-term desires, it’s not likely to cause financial distraction, dependency, or drain. And that’s just ninety seconds worth of solid good reasons :)