I would like it if she would have an affair for a while, keeping it secret from me, lying to me about where she is going and with whom, and then eventually spring it on me, telling me all the details when she had cheated me without me knowing. Maybe come home to me freshly fucked, drag me into the bedroom and frantically get undressed, spreading herself on the bed and urging me to kiss her there. Since all of this would be completely out of character for her already, I'd know right away that something exciting was unfolding. I'd love it if she'd wait until I'm eating her, and then asking me if I can taste his cum.
I think what I like so much about this scenario is that from then on, I would never know when she might be fucking someone. So any time she would be away, out with "friends", shopping, etc., I'd be hot as hell, wondering what my naughty wife might be up to this time! lol