Something else...

You can't believe it. You loved her, you loved her so much that you were willing to fulfill any of her fantasies, even letting yourself be dominated.

The part about including another man isn't even the biggest problem. The problem here is that she never asked you or gave you any options to stop it, you never had a safe word. Besides, she didn't even bring a stranger to cuckold you, since from her behavior you deduced that the two knew each other. Considering how she compared his cock to yours, clearly she'd seen it before, which means she was cheating on you.

You kept up your submissive demeanor for the time being, eventually you both went to bed. She continued to humiliate you. You knew full well that it's normal to give your submissive some love after something like this, especially if it's his first time. This was further proof that she neither loved nor respected you.

You still tried one last action, a very small part of you hoping for the best, even though the larger part of you already knew the outcome.

"Doe?" You called her softly. "I need you, baby. This is too much for me."

Hearing your pleading tone, she hugged you and comforted you, explaining that the man was in fact a complete stranger and that this was all new to her. She had never realized the hurt she was doing to you. She reminded you how much she loved you and she sweetly made love to you as a reward.

At least that should have been the reaction. All you got in real response was a few more humiliations and a reminder that she was your mistress and you were her whore. She never once told you that she loved you.

As a final attempt, you suggested her the possibility of telling her one of your fantasies as well so that she could pay you back. She just laughed cruelly at your "funny joke" and she made it clear to you that she was already fulfilling your fantasy by making you her whore. She explained to you that the man from before, her new lover, would soon be coming to live with you, at least after he managed to divorce his wife.

What she never knew was that you had placed a hidden recording equipment in your bedroom, with the intention of reliving the moment together. You intended to surprise her with the recording as a gift. Now it would serve you for your ****, both from her and from the bastard who humiliated you without flinching.