Warning, this is a long response.
There is no sexual abuse but definitely FoO issues that she is dealing with...
You don't know this yet. Unfortunately, you don't really know much at this point and that is the way of things. Several months or a year or more of MC and her getting IC and you may know enough to know that those FOO issues are not also sex abuse issues. I do this work professionally, and my personal record of hidden sexual abuse with a client is 60 years, and her husband didn't have a clue.
again I feel how does that relate to her conscious decision to betray me?
It isn't so much a conscious "decision to betray you" as it is "a conscious decision to do something to herself that also constitutes a betrayal of the marriage and spouse". This is not a semantic thing, it is fucked up thinking, in a person who is dealing with their underlying issues in a destructive manner. This may be hard to read, or even understand, but oftentimes the WS isn't thinking of the BS at all because you have become so unimportant at the moment. After the high of the sex act, in the aftermath, then comes the crying, the self anger, the realization of what really has happened i.e. "I've betrayed my spouse".
The sex thing is an issue for me I must admit - she and I were our firsts for everything up to that point. Now that has changed. It was something I cherished as it was unique to us. That's gone now.
Something honestly more substantial and worthwhile has to replace that. Truthfully, and anyone reading who wants to bash me on this feel free to bash away, "firsts" in sex is not that unique. The most unique thing is "lasts" in the acts, where someone finds someone that they decide to spend their life with and never stray. That, unfortunately for the marriage and marital partner, may be the spouse they betrayed and came back to. Sometimes that return takes place after a decade or more, sometimes it is a week or a month or less.
That said it took days for her to answer questions honestly - she was lying and in damage control before.
Hard to take, I know, I put up with lies for 9 years after the affair my wife had. In MC she lied so much that the counselor must have thought I was over-reacting to things. Lying is a form of protection, she is protecting something. It may be the affair partner, it may be her marriage, it may be you, it may be her ego, it may be many things, or all things, but that lying has to break down before she can truly recover and before you and she can reconcile. It will soon be 2 years since my wife broke down and stopped lying, and it came in a flood.
where all WW could talk about was AP in romantic terms that she has not used on me in decades.
All that was fantasy fog talk. Immature BS talk. He was a cheater, she was a cheater, they were destroying two families, and abusing their marital partners sexually...and affairs are a form of sexual abuse, make no mistake, which a number of counselors and authorities agree on this. Try this on for size when you think of this, because this is what it is.
Romantic WS's talking to each other in these situations are like Hitler and Stalin telling each other what "great leaders" (great lovers and friends) they are and congratulating each other and being great pals at the beginning of WW II, joining together to destroy Poland (destroy two marriages and fuck over their closest associates...their spouses) and several other countries. Later the US and Allies (the betrayed spouses) find out about it, but defeating the Germany/Japan/Italy (the affair root) is actually paramount and Stalin (your wayward spouse...for sake of argument...the other WS can be Hitler) comes back into the fold (rejoins the marriage). You reading it later, is like Eisenhower reading their private communications and saying "wait a minute, Stalin (your wife) never talked like this to me" and having to decide to swallow it in the interests of saving the world (the marriage) from destruction.
Yeah, Hitler and Stalin were two really fucked up people and destroyed their countries.
telling me that she was sorry, that she didn't want me to leave her, that she didn't know how to make it up to me.
Finally, she is saying something that really makes sense. She doesn't know, and she can't know, she has to work, and work, and work, and work, and work, on herself and the marriage, not on you, to try to save the marriage if she can, to figure out how to make it up to you, if it can be done. She may not be able to make it up to you. The marriage may end. Without hard work it will either end, or go on in worse shape than before.
Hope that helps with making sense of things.