Damien you kind of contradict yourself in post. in one you talk about having had a submissive and lost her, so you had a D/S relationship. In your next post you seem to contradict yourself by saying "He did say something about her not liking abuse from other men though...not my thing anyway."
Yani you talk about a sub who will take a lot of abuse as not being trustwortty. Imagine the trust they needto have to allow you to put them in that postion. Might I suggest you guys google some S?M sites or read books like "Screw the Roses, Give me the Thorns" or anything by Jay Wiseman., since a large part on any D/S realtionship no matter how physicaly intense or as you see it degrading, is NOTHING without a strong psychological component. IMHO the BDSM couple Dom seems toenjoy having her made to service anonymous cocks without any pesonal attachment to the body attached to it.
Perhaps after a scene & the hobbyist is gone, she punishes him for making her service someone sexually, since if as you said she is the one that sets the limits, then isn't she the dominant personae? All he does is hold her leash,which is pretty passive and cheers her on!. Another suggestion is visit a BD/SM club like paddles or check withsome of the professional dungeons to see if they have a submissive on staff, but in those cases there is NO SEX, just varying degrees of domination, restraint as defined by the Dungeon Mistress or DungeonMaster