Negotiate, negotiate, negotiate! To me, that is the #1 rule when making changes to a D/s relationship.
How do you feel about this arrangement?
Did you agree to it, or was it forced on you as a requirement of staying in the relationship with Him?
Was it made clear before you entered in the relationship that something like this would happen (you being excluded from his bed when another woman comes to visit), or was it sprung on you after you had already developed feelings?
It's so important to remember that slave does not equal having no rights. This is not 17th century America where your choices are obey or be chased by man-eating dogs.
If you Master truly loves and respects you, he will put your needs at the top of his list, even above his own wants. A submissive is a precious thing, not someone to be taken for granted or taken unfair advantage of.
I don't even agree that "ultimately it's his choice." Fundamentally, you're an equal partner in this relationship even though you're submissive. You CHOOSE to obey your Master's orders. You CHOOSE to serve him. You CHOOSE to be in a relationship with him. And He needs to know that HIS CHOICES could drive you away and cause you psychological and emotional damage, if you are not respected and cherished.
Gralson: my husband (works out of town).
Auto: my girlfriend (lives with her husband Zoffee).
The most dangerous phrase in the English language is "we've always done it this way."