I hate to throw cold water on this but I see a couple of red flags. She started having an affair ( cheating ) hinted at or pushed for opening marriage. Flag.
Then after the facts are known (cheating ) .... an email is discovered emphasizing the plan for bare back sex. Flag ...half flag depending.
It took 4 days for her commit to not doing that ......REALLY. HUGE FLAG.
Super big Flag. I dont know whats been going on in your marriage for the past 22 yrs but that would seem be a big violation of trust and the on top of that to push that violation of trust into your health seems CRAZY. Wildly short sighted.
I wouldn't be to sure about being placated....however the new guy might be into it and he's shared his personal views and stories and that's changed her mind.
I'd say don't get steamrolled....if something doesn't feel right ...say no. Time out.
You might want to meet and look this bare back guy in the eye to see if you want to take that risk. I'd say you need lots of trust rebuilding behavior before agreeing to anything.