I personally am okay with it. Of course I hope the MC dominates both later, instead of becoming her lackey as he has been so far with what she said at the end of the BJ, and by allowing the tie up and spanking which was a bit odd he would allow that, people he hasn't seen in many years, whom are at odds with the other person. For all he could guess is she would beat the shit out of her since she couldn't fight back anymore. He didn't even put any rules in place like no putting things into her, anything that would show physical damage, etc.