What would , do or say, is your husband ask you to have a Threesome , with a friend that you both new well.
I'm not married so this is probably easy for me to say, but I was once, and I would say "thank you for being so open and honest with me, it's that trust that will keep us both together for the rest of our lives,"! However, experience tells me that this 'desire' of his MAY lend itself to feelings of inadequacy and insecurity so maybe leave this fantasy in you head?
I've been here before and it really depends. I can say for myself personally, seeing my (ex) husband fuck another woman was hard for me. However, it depends on the relationship you have with your husband.