Would you be concerned?

What do you like about FF?

Hide his phone,if it`s on silent he won`t be able to find/hear it and you could look through it.
Then after a couple of days you find it and give it to him.
If he can be sneaky so can you.

Timetogo I like your thinking

You could also choose to not give it to him...

Sorry, I really think that there needs to be a long discussion between you and your husband, preferably with a lawyer present!
The way that he is behaving certainly would be ringing alarm bells, He is obviously talking about you behind your back with another woman .
Why are you still with him?
He lies, stabs people that consider him a friend in the back and displays no loyalty to you at all. By his actions, he is either having an affair with that woman or gambling in secret.
I have to wonder if both of their actions means they are trying to push you and her DH into walking away from both of your marriages- just so they wouldn't feel guilty. Believe me, I know, it is what my exhusband did to me !

Eviebeanz - Nothing because I can see straight through her even if others can’t although I have heard snippets from other wives in the wider friendship group that they don’t trust her.

Bashful in that case I really cannot understand why you still want to continue to meet up with/be part of this group. I think it might be time to be less bashful and more forceful and let your husband know exactly what you think and that you're not interested in his excuses.
It may be that FF and her husband have an understanding and that is up to them but not something you have to put up with

The other thing is that his male friend is a very kind, straightforward, loyal kind of a guy and why should he suffer?.
How would be suffer more by you not visiting?
He is already suffering nastiness from his wife, which is up to him to deal with, but you don't have to keep witnessing it.
Perhaps he'd even be relieved if you stopped meeting up with them as that would show you don't go along with the unpleasant behaviour.

Your own relationship with your DH is a separate matter.

It could be time to put your own needs and feelings first

It feels to me that at the moment your dh is having some kind of EA under the cover of meeting up as couples. What a coward if he feels he can kick off at home to you but not come out into the open about what is really going on
Are you frightened of him?

The next time a visit is suggested, I'd be inclined to say I wasn't going. After all your husband doesn't really need you there does he?
Keep your self-respect.

i don't understand your attitude, OP.
you seem fixated on this woman, and her bad behaviour, games and smirking etc.
so what. who cares. she's nothing to you, only an acquaintance.
but all this whispering and knowing your business is involving your husband. he is involved with her. he tells her.
he is significant to you. he owes allegiance to you.
he is the one you should be dealing with.
there seems to be some head-in-the-sand-ism going on.
what good is that doing you. is that how you want to live.
you are wasting your life.

Welbeck is spot on

Changing a remembered version of events, especially if you were there and know what actually happened, is typical gaslighting behaviour. He is trying to make you doubt yourself, don't fall for it. A gaslighter would swear black was white and its your fault its not yellow if it means they can get their own way.

Personally I think that this is why he kicks off when you raise the subject, he's trying to stop you raising it by subtly controlling the situation (the more he kicks off, the less likely you will be to talk about it)

You really need to finish the discussion with him, because right now, nothings been resolved.

Bashful In your comment at 20:33:09,you wrote
"The FF (female friend) has often mentioned things about me or my private life that I feel is none of her business. My DH must gossip obviously".
Surely this means that your DH and FF are in communication privately?
Yet, in your next comment you wrote that you couldn't find any evidence of communication between DH and FF.
So where is she getting the information about your private life?
Or have I misunderstood what you wrote?
If I were in your shoes, I'd be very, very angry. I'm not really sure what I'd do about it though.

Chapeau, the OP also said there are plenty of times when she wouldn't know where her DH is.

And he could even have a separate phone to contact the FF, if he wanted to.

If I had money and was in this situation I’d pay for private investigator to confirm or refute my suspicions. This situation sounds very dodgy to me.

Dilly is right it does sound dodgy indeed but maybe op isn't quite ready to face what the implications might be.

How do relationship get to the point when you think it inappropriate to question what happened. I would have done it there and then. When they ran the husband down just call them out. Any knowing looks ask why. If they made me feel uncomfortable I would driven myself home and he could have walked. I couldn’t be with someone I walked on egg shells with. Now you are questioning other things he’s done. Life is too short.

FarNorth Thank you - you have cleared up one question for me.
I do think though, that if the FF has details of Bashfuls private life, then who else but the DH could have given her the information?
If this was found to be the case then isn't that evidence enough that FF and OH are 'in communication' with each other?
Oh dear! I'm sorry. I realise I must come over a tad pedantic (or have misunderstood again.) I just think that Bashful needs to do more than just vent. If she continues to quietly put up with this intolerable situation it will almost certainly have a negative impact on her mental health. Concrete answers to my questions may help Bashful realise that she shouldn't just put up with this awful and upsetting behavior. She should do something about it for her own well-being.