Original Sin
Okay, I'm going to let you cum now, but you have to follow my instructions.
Firstly, I want you to remove the buttplug from your ass and put it in your mouth. Keep lying down while you do this.
Secondly, I want you to smack your balls hard once every five seconds. This is to encourage you to cum quickly, and you must not forget to do this until you cum.
Now, I want you to edge once more. Be very careful not to cum.
Once you've edged, I want you to cum. Stroke as hard and fast as you can, still smacking your balls right up until the moment of orgasm, but while you stroke this time I want you to use your non-dominant hand to hold the dildo in your throat. Do not remove it, even if you gag, and if it slips slightly then shove it straight back in as hard as you can.
When you cum, I want you to ruin it. I offered you a better experience if you gave me more time with you, but you declined, and so you are going to ruin your orgasm. Don't stop gagging until the orgasm has entirely passed, no matter how your eyes water.
Congratulations on your orgasm, slave. I hope you haven't spilled any, you know how I hate cleaning it up. If you have, lick it up.
Don't forget to thank me for allowing you to cum.