I had this problem, too, when I first started in BDSM with my ex husband. What I had to do was to show him that there are certain safety precautions that are taken when doing a scene that involves whipping, or spanking, or pretty much any kink for that matter. Set a safe word. Let him know that, if you use that safeword, that's when he needs to stop. Better yet, use the traffic light system. Red: STOP. It's too much. Yellow: Slow down or lighten up and evaluate. I need a breather. Green: Keep going or go harder. Orgasm denial is something that some people just aren't comfortable with. However, in my experience, if you tell someone that by denying you an orgasm now, when they allow it later, it will be so much more intense, they usually warm to the concept. It takes time, but they warm to it.