I echo the posters above that it strains credulity to suggest that you didn't enjoy sex with the AP as much as you did with your BH. I think it's negative to your efforts to heal your marriage to suggest otherwise. Did you lie to your AP and sneak around behind his back to create opportunities for sex with your BH? Nope. The person you lied to, and sneaked around, was your BH. People make that kind of effort and prosecute that kind of dishonesty to get some candy, some good stuff, something they really enjoy a lot. At the time, your BH was your sexual Plan B.
To that point, I think you also need to be honest about the fact that, but for the happenstance of the AP getting caught by his wife, the A would still be ongoing, you'd still be ramping up the fantasy aspect and the freaky sex, and all of this would be even at a higher level than it was. You did not end this A of your own choice.
Which leads me to another suggestion toward healing: create a detailed, written timeline of the A, cross-linked to dates of your emails and also to family events. Your situation is somewhat unique because your BH has already read your texts. What he doesn't know, though, is your private emotional and mental place at the various events during the A. One of the issues in healing from an A, especially a LTPA like yours, is that it creates an "intimacy hole" in the marriage, where you created a private intimate space that you shared with your AP but kept secret from your BH. One of the things most betrayed spouses struggle with is simply making chronological sense of the events of the A. After all, he was married to you, and from your description it sounds like you invested a lot of time and energy into the A. That time and energy had to be taken from some other part of your life. I'm guessing that, like most LTA's, you took it from your marriage.
Your BH, for example, will try to remember what he was doing the first time you were fucking your AP. He will be curious to know how that came to pass. What did you talk about with your AP to arrange that first fuck. What level of flirting and courting preceded it? Why did you decide to betray your husband at that point in time, as opposed to a week earlier or later, or a year earlier? Why that AP as opposed to any of the thousands of men who would likely be happy to have sex with you? What lie(s) did you tell your BH to create that first opportunity? What did you think and do the first time you returned home after sex with the AP?
These details will be very painful for your BH to hear, but they will restore intimacy and they may be the first honest thing you say to him (because, let's be honest, as everybody here notes, that bullcrap line about preferring sex with your BH over your AP, even during the A, exactly nobody will ever believe that).
I do agree that it would be a bad idea for you to offer a separation to your BH. I think your BH would see that as you giving up on him and running away from him. By the way, I'm editing this later and I do disagree with Bigger (below), for once. I agree with his concept in general, but timing is everything. Six months out from DDay from a LTPA with the kinds of details in yours, including the express and intentional sexual humiliation of your BH, is way too early to expect him to be able to engage with you in any sort of meaningful way. In fact, I disagree with Fenderguy that a year is the appropriate threshold. A year may have worked for Fender because that was his personal truth. But every BH has to heal from the initial trauma to some extent before being able to engage, and it is not unreasonable to expect your BH's obsessive questioning about the basic facts to continue for years.
To that end, I might add, the written timeline would probably go a long way toward truncating that process. It should be a working document that you revise and build as you remember things, perhaps often triggered by questions from your BH.
In the meantime, I think your only hope for R, albeit a slender hope, is to cling to him as tightly as you can and tell him that if he wants you gone he's going to have to physically push you out of the house. You have wounded his sexuality so much that the most likely outcome is that he will not be able to be sexual or loving with you, ever, even if he wants to. But on the slender chance that there might be a faint, flickering light at the end of the tunnel, that flame would be craving a giant expression from you, consistently and persistently, of love and sexual desire.
To this last point, I'm usually not a fan of what some here call the "grand gesture" -- something big a wayward does to make a strong, affirmative statement of sexual desire. But here I think you ought to at least consider this, though admittedly I have no idea what that might look like. The record of belittling and demeaning your BH's sexual prowess, that is going to be your biggest hurdle. It is fruitless to now try to say you didn't mean those things when you said them. Nobody is going to believe that. Your fruitful approach is to find the things in him that made you horny when you met and decided to marry, and amplify them in some way, with some sort of grand gesture (or repeated gestures) of sexual desire aimed solely at pleasing him and bolstering his sexual self esteem. My observation has been that women often under-estimate the degree to which a man's sexuality is highly fragile and will retreat if threatened or injured.
[This message edited by Butforthegrace at 7:45 AM, January 2nd (Wednesday)]