Overwhelmingly, the most important thing with a couple is THEIR dual comfortability with adding a third. She has to enjoy it for herself...doing it because he wants it, usually doesn't last, yet most of the time it's the hubby who sabotages it from being ongoing. Too many immediately start an inquisition rapid firing endless questions that may be curiosity/informational but always appear as mistrust or downright accusing. A lot of guys fantasize and make it happen but see the mutual enjoyment as too 'emotional'; I will acknowledge that I do care to the extent I don't treat women like a piece of meat. My worst experience was the husband I talked with for 6 months before we met, and as soon as she and I finished fucking he wanted to beat her up. The break up that hurt ME most was a wife I saw for two years; he and I hung out once a week most of that time. He was frustrated that he could not watch us once.....I didn't mind at all, but she said it would never happen and I was caught in the middle and he was a highly ranked law enforcement officer.