RTC. I will be at work today, so won't be posting.
Maths - whilst I agree with what you say about the contempt shown, the probability of affairs and also the logical next step i.e. forcing a showdown, I think there's also a bit of "gap filling" (and perhaps we're all doing that to some extent).
OP hasn't said that the nice things DH does for the family are only on his terms, there is no evidence that the dinner party was for HIS friends (OP just described them as "company") and it's not as if Ringing was completely banned from buying wine glasses. If providing glasses for friends had ever been more important to Ringing than having the "right" type of "white wine" glasses, she would have bought some from her allowance. Can you imagine having friends round for dinner and deciding that, since you couldn't afford to buy expensive cutlery or glassware, they would have to do without?
I do understand about social standing etc. and maybe it's because I left that whole "dinner party to impress" world a long time ago, but as I've got older, it's much more important to me that friends are comfortable and happy in our home.
It would be tempting to think of this man as an emotional desert, who only gets his kicks from his business and controlling Ringing, but other parts of his personality do not seem to fit with that assessment. To have wanted to leave 4 years ago suggests that this man once did feel emotions very strongly. He appears to adore his children, especially his son.
One of the things I dislike about the views expressed on Mumsnet sometimes is that men don't have the same emotional nourishment and love needs as women - and that men view their marriages as a means of controlling women and getting "service" from them. This reduces men to unthinking, feeling creatures and is not my experience at all.
I agree that your H has every reason to deny affairs RTC - and lack of time and accessibility are no bars to affairs unfortunately.
If you really don't think the good counsellor route, the letter or another conversation are going to work, perhaps shock tactics are what's needed - but given that you've said he'd cut his own nose off to spite his face, if you go down that road, be prepared for the consequences. It does seem as though he doesn't really take your threats seriously (i.e. open marriage).
Only you know what your tipping point will be, but I ask you again, can you stay with someone who appears not to love you?
Also, what do people in RL say - your families and real friends? What's their view of the two of you and how you interact?