I think that is one of the common misconceptions of poly/open relationships. Similar to the one I keep butting my head against. I'm a poly female, but I'm not bi! OMG! So the fact that you are not really interested in having a 3-some with your ladies doesn't make you odd, it makes you, you.
Life is about the journey and not the destination,
so what better way to know life
than to wander all the roads and paths set before you.