Honestly, LateNight, this sounds borderline sexually abusive.
I realize that you chose to indulge in the fantasy with her, so maybe you feel that she didn't do anything wrong. But there's a big difference between a run-of-the-mill cheating fantasy and something as extreme as what you describe.
You don't say if you explicitly consented to her locking your dick in a cage, gagging, shackling, or whipping you - maybe those are things that had already been part of your sexual relationship, it's not totally clear since these things aren't cheating fantasy specific. It doesn't sound like they were part of a routine to you. To me, those actions seem like extremes that a normal cheating fantasy doesn't go into. Not to say that cheating fantasies are great to begin with, but fantasies can be healthy outlets with two consenting partners- this one does not seem to be healthy at all.
There is such a thing as sexual coercion, and I can understand how it can be a blurry line for some people to see. We all want to see our partners turned on, so of course sometimes we indulge them in things we ourselves aren't into, but knowing that they're turned on turns us on. However there is a big difference between willingly doing something you dislike because you know your partner likes it, and doing it because you feel you have to for some reason - like being afraid that they might leave you if you don't. You whimpering answers to her while she berates you about your "inadequacies" sounds a hell of a lot like coercion to me.
I know we're all getting bits and pieces of your story as you've updated over time, so we're piecing it all together just as you are. But the cheating itself is already such a selfish abuse, add on the sex parties with her whole office, and now your experience of you agreeing to indulge a fantasy of hers, and then her taking it completely over the top - the level of disrespect she took this too is egregious.
If I was enough she wouldn't be doing this.
If I was bigger, stronger, taller, richer, funnier, traveled more, fucked harder, cared less not more, then I would be enough.
I know it's really hard to see it right now, but this is not about you. The kind of person who feels the need to do these things is FUBAR - Fucked. Up. Beyond. All. Reason! Your pain and suffering is yours to feel, and feel it you should. But it is absolutely NOT on you to take responsibility for any of her actions.
We know you are trying to search for answers. We all do. We assume it must have been something we did or didn't do. "I'm not enough" is the lie we all tell ourselves when there's no logical reason we can find. We start grasping at straws looking for anything that makes sense. It's our mind's way of trying to assert control over a situation that we really have no control of.
Control is an illusion. No amount of answers will bring you the control you seek, because ultimately what you want to control is the outcome, and that is a level of control you will never have.
Months after DDay I scrounged through phone records, texts, and emails to create a timeline to attempt to make sense of it all. And there are still huge gaping holes in my knowledge of the situation, and I don't have any more control than I did before I began the scavenger hunt. There is literally no reason good enough to do what she did to you.
Please take care. You're only a few months out, so be patient with yourself. Drink water, get some sleep!
I also just want to emphasize the points made by RocketRaccoon and OwningItNow below.
Why do you need affirmation from someone that has failed and betrayed you? If you want affirmation, let it come from a source you respect.
She does not fucking deserve you. Her opinion means nothing.
It is my opinion that you have never seen this woman clearly. Do you have family, LN? What do they think of her? Where are they in all this?
Please ask for help from friends and family. No matter how embarrassing you feel it is, the people who really love you should be there for you no matter what. I honestly would not have survived if it weren't for my family and a few close friends. They can give you honest yet loving feedback when you have questions, and also just a shoulder to cry on when need be.
SI was also a godsend for me. There's nothing like screaming into the abyss of the internet to get you through the tough times.
Have you been going to therapy? My XH is a sex addict, and as the spouse of an SA (especially one who would not seek treatment like my XH) I have an abundance of unpleasant experiences that I had kept bottled up for many years. Going to therapy and talking through those experiences with a compassionate person was/is very freeing. That release you felt by finally typing out your story, you could feel that regularly if you had a safe place to discuss these issues.
Of course SI is a great place for that as well, but be aware to preface any overtly sexual posts with a TMI in case they might trigger other members. Many of us have dealt with spouses who have various levels of perversion like this, and it is helpful to talk about it with other people, even if it's just to say "holy shit, I can't believe this happened to me!!" But I always try to stay mindful that others might not be prepared to read our experiences as they can be extreme.
If you can't afford regular in person therapy, there are some great online services. I have an online therapist who has been with me since about 2 months before DDay so she's seen it all, and having weekly 30 minute check ins with her via video call is really helpful! I can also text her through the app anytime I want, and she'll get back to me when she can during her normal working hours.
It's kind of nice to know I can just spill my guts when I need to, even if it's 3am because I can't sleep. And her responses always cut right to the quick of the situation - I could write her 4 paragraphs of word vomit, and she will come back with one really insightful question.
I also see an in person therapist who specializes in trauma, which I find to be very helpful. You can interview therapists until you find one you like - mine even talked to me over phone call at first to see if we would be a good fit before I came in to see her.
Stay strong. Vent here if you need to. We understand.