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Can he keep from cumming....
Tell him that you will jerk him for a set number of minutes. If he can not hold back, he will cum all over his own face...
Start jerking him, and after short time place the powerfull vibrator to the buttplug so the vibration will move. Keep jerking until you see he is close (DONT LET HIM CUM!), then stop...
Tell him he made it and the reward is that he will not cum in his face,
However... tonight he will not cum at all!
Look at the disappointment in his face. He is wondering if you will stick to it...
Lay down next to him and have an orgasm, take your time, and be really vocal. Tell him how good it feels.