Then she lets go of your cock and says:
"Now it's your turn! I want you to start nice and slow, like we did last Saturday. Use plenty of lube, and be sure you constantly have pre-cum dripping on the mirror!"
You groan, but start stroking. You know from last Saturday that this is torturous. At least then you had permission to cum whenever you wanted. But this time you have to hold back, and also keep on the edge enough to drip pre-cum on the mirror!