Whatever sense of power Robin felt holding Xavier's balls as he fucked his wife, he felt a nearly equal measure of submission.  As if the conservation of energy law applied to the power dynamic between the three of them.  The inclusion of this third variable in the equilibrium equation between man and wife somewhat destabilized what had become an overly dull and predictable relationship.  It was invigorating in it's own way, unfamiliar yet not unpleasant, much like the sensation he got from Robin's thumb pressing against his sphincter.  Robin was correct about permission, Xavier wouldn't have given it in a million years.  He was already giving them a bit of a stern look, though Xavier was never likely to use the safe word, he would just physically stop them if they went too far for him.<br/><br/>Robin's firm grip on his balls kept his thrusts into Abigail slow and measured, as if he was careful to let Robin set the pace at which he enjoyed his own wife.  The sense of restraint was both incredibly frustrating and highly erotic.  His cock throbbed inside Abigail's wet cunt, her flowing juices attesting to her own arousal.  He had settled into an almost comfortable sort of rhythm, lulled into relaxing a little when without warning Robin's thumb slipped inside of his ass.<br/><br/>Like a goaded horse he thrust forward, his hips slapping noisily against Abi's bottom as he sank deep into her with enough force to make her ass jiggle and her boobs sway.  The sudden increase of speed also meant Robin tugged at his balls a bit harder, though more accurately it was his balls tugging at her hand.  He half moaned and half grunted as he was sent over the edge.  Despite the tugging on his balls he gave several more deep thrusts he gave Robin a look that for a moment was stern and reproachful but he couldn't maintain it his jaw opening and another moan of pleasure escaping his lips.  He was very near to climax even though he had intended to draw things out more.  He had been eager to feel Robin's lips on his shaft once more along with the feeling of dominance getting oral often gave him.  But that dynamic had shifted considerably though he was hardly at their mercy, they certainly made a good case of his submission.  A feeling he had never really had before.