My ex, affectionately know as the ironbox, did start getting suspicious of me later in our marriage. Foreplay to her was dinner, a movie, and two weeks of begging. She was so frigid when she did take her clothes off the furnace kicked on so needless to say we didn't do it very often. And in those pre-internet days good porn wasn't as readily available so on those rare occasions that we actually did screw she did start wondering where the new ideas came from. I calmly told her since I didn't get it but twice a year I have lots of time to think about it. And she was dumb enough to believe it!
Fortunately for me my current SO watches lots of porn while I'm traveling so I'm now learning from her. At least I hope that's where she's getting her ideas