I was a slave for 4 and a half years. Spent a good bit of time in LA area dungeons with my Sir. I sometimes saw what you noticed at the dungeon, a seeming lack of desire in terms of one person longing for a specific other. I certainly felt that longing, for the man I served. It drove a lot of what I did. But it may not have been apparent to an observer. I think scenes also can be very different based on the depth of the relationship between the partners.