Looking for story

[throwaway21]

So I remember reading this story relatively recently(maybe within the past couple of months). I can only remember a few key points about the story:
- Starts out with two dominant females, and submissive male. They all know each other, and are friends(I think)
- One of the females is normally more timid, but is a little more dominant when they play, and really wants him as their slave/pet.
- The two gag the male and put a urethral plug(which had like a cap at the end, forcing his ejaculate to build up inside) in him
- The two dominants take him outside(like pet play maybe) and a stranger sees them. The stranger is interested and it gets in on the action.

That's about all I can remember from the story. Any help would be so great!