Your girlfriend... pounding Olivia?

You are stunned when you enter the room and find your girlfriend mercilessly pounding Olivia with an incredibly realistic strap-on, your roommate moaning uncontrollably as a result. Both of them are completely naked, with their hot bodies fully in your view as you are too stunned to react, while also noticing that Stacey seems rather angry at Olivia.

"You think just because I told you about it you can make me your ****, bitch?!", Stacey yells at Olivia as she moans in return, and you realize there is quite a lot of marker on both their bodies, some of which you try to read, still too stunned to move or try to speak up.

What even happened here? You ask yourself as you manage to read OLIVIA'S MISTRESS and BIG COCK on Stacey, which makes you realize the dick is actually real, not some fancy strap-on she bought, much to your utter shock, as you never imagined the marker could do that much, while on Olivia's back you see COCKSLUT written in big letters, as well as several smaller things that you are unable to read. It doesn't seem either of them notices you are watching them, too focused on what they are doing.

However, you can see two words written in VERY big letters across Stacey's back, which explain why she is being so aggressive towards Olivia and talking to her like that, MEAN and DOMINANT scrawled over her back rather sloppily. The exact position of the words and the angle they are at means that only Olivia could have written them, as it would have been impossible for Stacey to write them herself on her own back, but you can't help but question why she did it. Did Stacey order her to once she had her under her control, or did she also want this deep down, to be punished by a dominant Mistress Stacey couldn't act like, and did it on her own without being asked to once the tables were turned and she was made into the ****?

"S-sorry Mistress, I w-was a bad g-g-girl for trying t-that! P-please f-f-fuck me m-more!", Olivia responded, moaning more and more as you slowly made an image in your mind about what might have gone down, likely related to the marker. As undoubtedly hot as it is to watch Olivia getting absolutely railed by your girlfriend, you speak up, wanting definite answers.

"What the fuck is going on here?!", you yell, and Stacey suddenly stops and looks back at you, a stunned look on her face.