to be honest, i can't speak for your wife. i imagine you know her better than anyone else could possibly know here on this site.
speaking only for myself, i really enjoyed exploring fantasies with my husband. it took me a while to consider another man in those fantasies but once i did, i found i really enjoyed them very much. he's a very skilful storyteller and puts great effort into building an imaginary fantasy scene, describing the other guy, describing my feelings, describing the slow seduction process, the complex emotions, the teasing, the surreptitious glances, the feeling of being overcome and overwhelmed, that moment of wildness where i can find myself being someone else and losing all control. i would totally get lost in all that. to the point where i'd always ask him to to describe another fantasy each time we'd get to fucking. and i'd ask to include other men. more men. big men. several men at the same time. it helped me discover what i really enjoyed. it helped me understand my own fantasy and sexual preferences.
women love that stuff. help her find that sexual side of her.