No need to feel ashamed, we were all young and I think most people have some brush with infidelity sometime between high school and their thirties... at least that appears to be the norm.
I guess you can get a lot of benefit from this too... you very likley KNOW what your H is telling her that's a lie. You CAN properly INFORM OW of these lies if you chose to confront her.
You sound like you have quite a bit of support already and have exposed to a certain number already.
I am wondering actually... I will have to leaev this to the people who have been to Retro. to answer but...
Maybe Retro wont HELP when an affair is happening... but is there a high risk of any DAMAGE being done to the marriage for going to retro under these cirucmstances?
I am wondering now.. can it HURT?
Out of curiosity P, how many affairs has your H had in total that you know of? He sounds like what Shirley Glass calls a "romance addict"