IMO if something big is missing in a marriage a couple may turn to this dangerous amusement...I think it is called "boredom"...Sexual fascinations should have ended prior to marriage or partnering....But it didn't....So here, I believe you are walking on hallowed ground...Just make sure that something said in the throes of passion, does not exceed it bounds....Be sure that each of you know where the "brake" button is...This way, years from now, you will also be able to say....No regrets...
My personal opinion is that I see no good that could come from this...Not as much the man, but the woman....A woman's sexual awakenings are much deeper than a man's....What if she finds a new and erotic stirring being sexual with another woman?....Or perhaps a "bigger" man?....Pandora's Box will have been opened....Will she ever be satisfied again just being with a man?....These are just a few of the things that I would ponder in thinking of this happening....Then the other woman....Will she be more sexual than you are?....What if her sexual know how can stir him more than you do?...You know we are all different in our approach to sex and lust.....A woman's eyes can tell the story to a man without speaking and this certainly would be a fear in the back of my mind.....In essence....Am I good enough to hold him or will she do to him something that I could not do?
Myself, I would never let another woman at my man....He is too good a lover....Actually great.....Saying this, if I want a good fix I will go to the "Land of Fantasy"....Here in my safe house there is no harm done and it makes for one heck of an orgasm.....Fantasy is wonderful as long as you remember that IT IS FANTASY....Trying to act it out is where you can get in trouble...
Just my thoughts,
Caroline