Hotwife?

I've recently been researching the term "hotwife". "Obsessing" is probably a better term for it. For the last week I've been thinking about my wife getting pumped by a cock that isn't mine. What is it that makes this a turn-on? I doubt I could ever allow her to act on this, since I would be worried about losing her, but I can't get it out of my mind. My options at this point are to either share my thoughts with her, or bury them and try not to let them surface. I'm leaning towards coming "clean". We've always had an honest relationship, and I think I need to tell her about this....