I think the Wayward has the right to know, especially if he is in recovery and you are in R, but nevertheless is his son too.
He is a young adult at 18, he can have this conversation and I understand him for feeling resentment to his father, he broke his moral compass but also the image your son had of Dad. Which was likely idealized, not that of a cheater.
And for your son to truly understand the dynamics and consequences of the betrayal of his father, he needs to acknowledge it and confront it, or it could bite him ack or even leading him through the same path as a paradox, in the future.
He is young and grown up to talk to dad about his feelings.
However he does not have your maturity.
The ideal scenario is that he can talk directly, but emotionally he might need a help from you and from dad too.
Is delicate matter, painful for you too.
What I would do if I were in your shoes:
- Speak with my son and tell him openly, I think dad needs to know, and you should tell him. But this is a delicate emotional topic, are you ok if I talk to him first and then we try to arrange a face to face with dad. If you two want me present I will be here for both of you. I want you 2 to confront your feelings, because this is painful for you and your father and as grown men you need to face it, not hide it.
- If the son agrees for you to mediate good. If they both want you in to help navigate this emotional minefield even better.
- If he doesn't talk with him again and convince him is critical to talk to his father as he is trying to heal and amend to his mistakes.
- If he wants to talk alone you need to prepare him, to express his disappointment but also understand he still needs to respect his dad, he made a mistake, admitted to it and now he is owning it by working towards becoming a safe husband and father. And that is admirable
Probably the best would be that both parties are prepared by you, because is going to be high on emotions and that for men means anger, it could escalate to say things to each other they might regret.
But you probably need to suggest to your son that you feel important, for the process of healing of both parents, and in reflection the children, if you first prepare your husband and then they talk to each other.
Stuff under the rug, of this magnitude, is never good.
ANd the WS has the right to know, even if painful.