How would you handle this?

I hope for your advice on the following situation.  Sorry if it looks like a long story, but it is all relevant ;-)

I have a group of friends, we are 5 couples, who have known each other since high school.  Now we're in our early fifties.  We have had many parties, holidays, outings, etc. throughout all these years.  On New Year's Eve we celebrated together and had another (last) wonderful night.  On New Year's Day, during breakfast, one of my friends (call her C) decides to take a look at a website to see if the mother of the dog she wants, is already pregnant, while her husband (call him P) goes for his shower.  She clicks on Facebook and Messenger is on.  There she reads his correspondence with one of the other friends (call her B) in our group.  They arrange to meet up without their spouses knowing.  When P comes back from his shower C asks him what is going on.  To make a long story short : first he denies everything, but in the end she learns that P and B have been seeing each other for 15 years!!!!  Nobody had a clue, including V, B's husband.

C, understandably, is completely confused, sad, angry, ...  They have been together for 34 years, they were each other's first boy-/girlfriend.  So she comes over to me and tells me this story.  Se says she wants confidentiality, because their three daughters don't know yet and she does not want them to find out through some stranger.  So, of course, I keep my mouth shut.  I even pretend not to know when B's son refers to it.  This already does not feel right to me, but I really like my friend C and promised her confidentiality.  As time goes on, C tells her story to other people (people I know, people I don't know ...), but she does not tell me I no longer need to keep silent.  She kind of pretends to P that nobody knows, but, of course, he's not stupid and can guess why she's meeting up with me, and all the other people she told in the meantime.

So, the other day, we arrange to go for a walk together and I go pick her up.  She asks me in and in the hall, just before entering the living room, she whispers : "Pretend everything is normal!"  I enter and P is sitting at the table, right in front of the entrance.  I say hi and feel extremely uncomfortable, so I avoid looking at him.  As soon as we're outside, I realise I usually kiss him to say hi and this time of course I didn't, because I couldnt think straight.

I really want to do as C asks me, because she's a good friend, but this is getting ridiculous.  Now I am so confused, even if I don't try to act the way C wants me to, I don't know how I want to act myself.  On the one hand, I think he's a lying pig and he hurt her so, so much.  She's a real housewife, her family is everything to her ...  But on the other hand, he did nothing to hurt me.  He used to be the friend you could count on, even though he has a difficult character.

The same with B.  I haven't seen her since New Year's Eve, but I do go on walks with her husband, V.  I try not to talk about C and P to V and not to talk about B and V to C.  That is the easy part.  Everytime we part, V tells me to say hi to my husband and I know the thing to do is also to say : "say hi to B.", but I just can't!!  I told V I did not know how to act (he knows I'm autistic, but minimises it all the time) and I think he understands, or doesn't mind too much.

He does tell me that B is scared to leave the house, because she's so ashamed (bit late, according to me ...) and he asked me what I would do if I ran into her.  I told him I'd probably say hi and leave it there.  I never really liked B too much.  She is very introverted and I know nothing about her private life (she has a son and I don't know who is the father e.g.), but I respect that she does not want others to know her stuff.  And again, she did nothing to harm me, but she did hurt my good friend C and my friend V (her husband), so how can she be a friend of mine??

Please, anyone who has good advice to cope with this situation, let me know!