If V were Starsky and you were a new guy on the board then I would be saying that your H sounds like he is in at minimum an EA or PA with the 'friend', or she may be a POW in the wings. This may explain a few things. I say this to be kind Msd as I believe in Intel.
From my sitch you will see that I tackled this aspect of an infidelity head on with POW (a 'friend' of H) and H directly. Msd you need Intel, and under normal circumstances the 'if you snoop, you will get poop' rule applies, but in this circumstance I believe you should know. Can you check phone or email? Pink followed her H to uncover the waywardness. OD found documents. V made direct challenges to H and POWs.
Starsky, Wonka if you are about can you help a little as V may not be putting across properly, but I think this may be the case and worth checking out. H may be gaslighting Msd.
82% of affairs start with friendship Msd. Friendships between opposite sexes are difficult territory and often the other person is a trade down. The key research paper is by Shirley Glass (sadly died of cancer and her site is now a memorial to her wonderful work) and I have her research paper but can not find it on the internet.
Her book arising from it is often quoted.
If this is infidelity then you can lance this sore. The main link I can find is:
