From my point of view, as an individual who has yet to experience either a long term relationship or sex, perhaps I would feel a touch cheated because it would claw at my own insecurities arising from own self consciousness and image. Perhaps then I would it would go through the motions shifting from anger to rationalisation; after all, she did choose me for the last 20 years meaning it went well beyond just sex. Still, perhaps a small part of me would nag asking whether she hooked up with me because I was not only as good as the rest in bed but adept at other facets of factors that holds relationships together (ranging from personality to skill set) or whether I was just good enough to have more than compensated for my, perhaps average, sex skills (remember this is all going on in my head without any knowledge as to how good or bad those other guys were and asking her would perhaps make me look pitiful) with the rest of aforementioned aspects. Perhaps, later would come the moment of disillusionment in knowing that nothing has truly changed and that that secret affected nothing in our marriage and that my wife has enough faith in me to move past (immediately or in time) the reaction to the information she may have thought was a burden to her and wanted to share it. I would have gained perspective from this somewhat uncomfortable knowledge knowing we both dedicated our lives to each other and that my wife would not trade in the past 20 years of our marriage to screw many more random guys.
But hey, what would I know, I am still a virgin.