Life is better with sex, and sex is better with fantasy.
With fantasy I can be a king, a prince, a bird…
what s wrong if I imagine my wife kissing other men, or having sex with many other ?
To a point. Fantasy is fantasy and reality reality for a reason. While some fantasy can add an element of eroticism to a sexual experience not all fantasy works in reality with how you envision it or plays out in your head. When real emotions and people's own thoughts are involved it often times get complicated. Not to mention some fantasies aren't exactly morally appropriate.
I can fantasize all day about women getting slutty and taking on several men, but in reality I know not many women want to or even willingly engage in such promiscuous behavior. Nor would I like it if someone I was emotionally involved with engaged in such behavior.
But hey if you like seeing your wife kiss other men and she also enjoys it. Knock yourself out.