I agree with BraveSirRobin that you deserve kudos for taking the first step of telling your BH the deets.
Here is the thing, though, that other posters are noticing. R is really hard. Like running a marathon on a scorching hot day with no water. Like the hardest thing you've done. We wonder if you have the heart and the desire and the strength to do it. You have to really want it. Among other things, you have to make yourself humble and transparent and devoted to your BH.
You should expect him to ask questions about the sexual and other intimate details of your A over and over and over again. This is a very common thing for BH's to do. It's not because he wants to rub your face in it. It's because he's trying to wrap his mind around that intimacy continuum, the one you stole from him and gave to another man. He is trying to embed it into his own linear memory as if he lived it, so that he restores the continuity of his knowledge of you.
I fact, you should worry if he doesn't do this. That's probably a sign that he has stopped caring.
You should expect that his emotions will be a roller coaster for a long time. Like even up to a year. One of the emotions he will cycle through will be anger. It will likely be a deep, profound, hate-filled anger, enough to frighten you that he might harm you. He may use awful words like "slut" or "whore" and he may say that with venom, like he really means it, looking you in the eye with his own eyes burning with rage. You should be prepared to accept those bouts of anger with humility.
Your sister is an enemy to your marriage. Period. I understand that you are tight with her, and have roots. But she is also your BH's family, and she betrayed him when she failed to take steps to stop the A and/or failed to warn him. She also betrayed your marriage when she did those things. By extension, if your marriage is important to you, she betrayed you too.
It is quite possible your BH will loathe and resent her for the rest of his life. She deserves to be loathed and resented by him. You should expect your new reality will include making sure that there are no family functions where both are in attendance.
As to your toxic friend, not related to you, all of the above, times ten. She is an enemy to your marriage. At some point you ought to decide whether your marriage or your toxic friend is more important to you.
Through it all, remember that you do him the greatest honor by being honest. If you don't feel like you can remain humble through his rage, be honest about it and leave him. If you feel an urge to elevate your fealty to your sister or your friend over your marriage in terms of importance to you, do him a favor and tell him this so he can have agency to make his own decisions about what he wants to do.
Keep in mind this. My observation here on SI is that most women significantly underestimate the profound degree to which the sexual humiliation and emasculation of a WW's PA injures a BH. It cuts to his very sense of himself as a man. He may ask you questions about what the AP's penis was like, whether you enjoyed it, why you decided to go back to it again for another helping, etc. He will likely be trying to reenact in his mind exactly what was going on at home while you were having sex with the AP. What was he doing when you left. What lie did you tell him about where you were going. Did you kiss on the way out? Was he doing dishes or reading the kids a bedtime story while you were on your knees giving head to another man? Did you kiss when you returned? Had his dick been in your mouth before that kiss? it would be normal for your BH to be thinking about stuff like that. My observation is that most BH's think through that level of detail.
My strongest possible advice is: do not try to minimize or avoid any of this. If you had orgasms with the AP, be honest. If you liked the sex, be honest. Again, your BH will feel respected and legitimized as your husband by the frankness and honesty, and this will outweigh the hurt he feels.
Also, no matter what, do not try to say anything like "it was just sex". Women say this a lot, and the reason they say it is because they fundamentally misunderstand men. For betrayed men, this is among the most hurtful things a WW can say. The BH isn't worried about whether you enjoyed the sex. If you went back for seconds, thirds, etc., you probably did enjoy it. What hurts him is that you invested time, energy, imagination, etc., even to the extent of lying to your BH, for the purpose of giving sexual pleasure to another man. By saying it was "just sex", you make it seem as if giving sexual pleasure to another man is a normal thing you would do regardless of being married.
What his mind will be doing through all of this is trying to wrap itself around the magnitude of the sexual humiliation part of your A. Whether he can get past it or not. A big factor in that calculus is whether he feels in his heart that your desire for him is true. So show him your desire, in the strongest possible way, as often as possible. I can't emphasize that enough.
Finally, the corollary to this is that R will not work unless your BH believes in his heart that your love, lust, and sexual desire for him as a man is deep and true. More important, deeper and truer than your sexual desire for your AP (or, in the parlance of SI, your desire to trade sex for the good stuff you felt you were getting from your A).
I do wish you luck. The tone of your initial comments, quite frankly, made some of us feel that you lack the depth of character needed to R successfully. I hope you prove us wrong.
[This message edited by Butforthegrace at 5:05 AM, May 16th (Thursday)]