When you tell him
This is the rough part. You have to insist that he comes in 25 seconds. That period might last a few months but it is heathy. Tell him that when he strokes he turns you on so you need some pictures of him doing it so you can masturbate. (take some pictures of your milking sessions too).
Try to increase his need to fulfill his dream (if it is anal, show him your ass while he is stroking; if it is blowjob, approach your head very close to his dick...).
During this period, I want you to workout, go to a gym or whatever you want but be sure to have a goddess body.
During his milking session you can use a rope tied around his cock and balls to make it hurt.
When finally he has cummed in 25 seconds (or 20 if he has been a bad boy again), you may continue
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