We've reached the most difficult part of your training, slut. But it will also be the part that will ultimately prepare you for what your life will be from now on: horny and hard 24/7, ready for your girlfriend whenever she wants.
Lay down on your back, crank up the speed of that vibrator to maximum, pump it bigger 2 or 3 more times, and stroke as fast as you can for the next 10 minutes. You must not cum, and stop briefly for 5 seconds every time you get to the edge. Gather any leaks of pre-cum with your other hand, don't stop while doing it, and take it to your mouth. Swallow it.
That's it! Are you ready for the ultimate challenge? Then go!
After 10 minutes have passed, you may go on. If I'm not covering my tits, you get to cum!