Not 100% sure what triggers it, but I've experienced it multiple times with my wife when she is involved seriously in an affair, and I LOVE it!!! When we are intimate she is constantly fantasizing that she is with her Lover and WOW the sex is AMAZING....even though I am just a "living dildo" at the time........and I vascillate back and forth between that angst feeling and absolute ECSTACY knowing how badly she wants him and I am helping her "experience" that desire at the time. And reading their emails, texts, chats (when she lets me) and seeing her write her desires for him and desires MUCH srronger than she ever expressed for me.....WOW!! CWI have heard these same words. I wonder what triggers this need in our wives?! It triggers both angst and is strangely satisfying as well.