I would love to have a threesome with my wife and another guy, had the opportunity once, our friend had suggested it but she didn't seem enthusiastic so I said I didn't think it was a good idea as I didn't want her doing something she might regret. It wasn't until I was thinking about it afterward that it occurred to me that she probably did want to but had wanted me to be the one to say yes because she was worried what I might think if she had said yes and I didn't want to.
I regret not realising that sooner, I think it would have been amazing to watch her with another guy. I know that there was something going on between them anyway, they had had sex on at least one occasion and she had sent him various sexy emails and pictures but she doesn't know that I know about that.