Why do married men dream of other women other than there wife?

Regardless of whether they are men or women, all people at some stage or other will have sexual fantasies.

We have sexual fantasies of other people because we have genetically evolved to reproduce from the bes possible and widest variety of stock. Dreaming of this is one way our brain has adapted to achieve this.

The evidence is that we don't just choose anyone to partner with. Most of us are selective to some degree.

Dreaming of sex with others doesn't mean you don't care for your partner, it just means your body knows it needs to reproduce.