I'm the MoG, I don't know the answer and not sure what "feels" right. B&G have said the decision is mine and they're happy with whatever makes the day best for me.
DH died when DC had just become adults. Over the years I've often thought their weddings will be tough on all of us because their father would be absent, and whilst I'm thrilled for DS, I expect to find the day difficult. I have been seeing a new man for about a year and in many ways have moved on, but I still find the loss of my DC's dad very difficult.
New man is lovely, well liked by DC and makes a good effort with them, but it's in a relaxed uncle or friend of the family, who you don't see very often kind of way. He's not a material part of their lives, has never lived with them, doesn't live with me.
If he sits at the top table it will be as company for me/to balance the seating arrangements, rather than because he's significant in DS's life iyswim.
Fwiw, NM has much better social skills than me and can keep any conversation going, whereas I struggle with that at the best of times.
Otoh, I've no idea if this relationship is going to last (it's great atm, but I have no ambition to remarry, for example) and it doesn't seem quite right to give such significance to someone who's small part in DS's life could well be transient.
WWYD?