I don't want to be exclusive to my partners but I want them to be exclusive to me.

How do I maintain that relationship? Obviously it doesn't seem "fair" that I get to sleep with multiple partners and none in my harem do, but that's what I want.

Have any of you accomplished this?

I know two of the four girls I'm regularly sleeping with are sleeping exclusively with me, the other two I assume, have partners. How can I get their exclusivity?