Slaves who love one another should have an option to share their personal room with a lover. This allows them to not constantly be bound to sex on the MC's part and lets them take care it themselves.
Another way that takes less micro-management: If a girl has a private room, then at day-end she should have a chance to pick a random person with whom she has a good relationship and let her join in the private room for the night. If she does that, they both lose x lust.
