Why don't you just stop having her boyfriend spend the night??? It sounds as though she is having a hard time transitioning from being intimate with him to being intimate with you after each night. It's your house too...no more overnight visits. You pushed that rule (which is great and shows flexibility) but it isn't working.
Of another concern is your rule number 6. It's easy to say either one of you can say stop (essentially a veto power) but what about the other human being's heart involved? I'm not slagging you but this type of rule makes anyone who comes into your life seem more of a casual play thing than a person. I guess as long as you are upfront about this rule and any potential partner is also good with it then it's fine, but if it is not something they are aware of you are somewhat deceiving them.
Playing the Game of Life with Monopoly rules.
Monogamy might just be in my genes
Poly Events All Over