Well.. I have "just" a gf (means not a wife), maybe it is not the same. But anyway I would never want her to have sex with somebody else. That doesn't turn me on at all. But that is just my way of thinking.
Some people do "share" their wife without looking crazy or having a weird relationship. Not many of course. But some do.
Anyway, even if it never happened before it's not like you are not allowed to do an exception. If you, your wife and the 3rd man sexpartner all agree to do it.. Why not?
But don't scream it out too loud. People will quickly say things your wife is a b**** or that you are an unsatisfying loser, etc. Because of that.
Watch out because once such a thought is made, you can't get rid of it.