I wanted to ask you what you would do in such a situation or simply what is your opinion about it.
How would you feel if your partner told you that he or she was planning to meet with a group of EF members but later on, after the meeting, you find out that it was actually a private meeting with a person of the opposite sex, someone you do not even know? Would it be completely fine for you? Wouldn't you ask yourself a question: why your partner simply did not tell me about feeling like meeting with someone? Why the story about a group of people where in fact it was a meeting with one person? Wouldn't you feel a bit strange?
Let me know what you think about it.

I wouldn't be happy! If it was innocent then why lie? Unless of course your partner planned to meet the group and only one turned up?

is this a rhetorical question?

Possibly they were doing something they didn't want you to know about (or hoping to) or it was completely innocent but they didn't want to jump through hoops to be allowed to go.

Maybe something else...

i think the best would be to ask you partner. anything what we say is only guessing...

Were they expecting to meet a group that turned into one, or the whole group thing was a decoy, and the one on one meeting was planned all along?

This doesn't necessarily mean anything sinister still.

I had a girlfriend who was very insecure. I loved her to pieces but the trust issue was a problem and caused many issues. Over time, I lied/bent the truth for the lack of hassle and stress in certain situations. For example, I would cite meeting a group of friends if I was with a friend who was a girl from work or other and we were catching up.

I did this purely bacause despite the meeting(s) being completely innocent, I knew my girlfriend had so many issues that it would cause arguments and accusations when I had done nothing wrong. I am not going to not look, talk to, or associate with other women, whether in a sole or group capacity, because my partner who might be wonderful in so many ways and love dearly has her own issues with trust, insecurity etc.

Not making any accusations here, just giving example.

If in doubt dump his sorry ass!

Get the popcorn y'all, this is gonna be thread of the day!

It admittedly sounds suspicious, but it could be easily explained, especially if it was a group meet-up in which all the other participants canceled or were no-shows.

If this is the first time something like this has happened, I think you should talk with your partner and give him/her the benefit of the doubt if the explanation seems plausible and you have no other reason for suspecting the possibility of an infidelity issue.

Meanwhile, maybe you might want to go along with him/her to the next meet-up.

I think the issue is - if your partner was going to an EF social event, then why didn't you go too, since you are also a member?

His? Why do automatically presume it's a guy who's done anything wrong? You know, women do wrong stuff as well.... been there, witnessed that (sadly)

Quite right.

But I suspect OP is woman too.

Could be wrong, just the manner in the writing and scenario, seems like a male thing to do in terms of subject matter, and an issue a woman would raise in such a way and place.

Apart from the answers above, which are valid in my opinion, I would ask the question: How did he or she find out? Was this some attempt at control over his or her partner?

But yes, hiding the truth often hurts more than telling the truth itself...

Just how many people did you think were in the grynch fan club?

All I can say is:

Well, six, according to his profile

You need to go back to your wife and ask her for the full facts before making any conclusions or listening to any opinions that will only serve to further erode any trust you have left in her.
By the way, how did you find out she had a secret rendezvous?

well obviously he wouldn't say anything because the other person would probably make a big fuss and blow everything out of proportion as usual. easier to have the quiet life. he unfortunately didn't bank on being under surreptitiously surveillance.

What if they were planning a surprise party for you?

at first sight it seems a bit weird, I would ask your partner about it

Hum.... Depend a lot on the circumstances.

It could be that others didn't show up or he went behind your back to meet a girl.