Can married men have women best friends?

We've all heard it before "she's just my friend" but can a man in a serious relationship or one whom is married have a woman as a friend? It's already hard to find love but staying in love is the battle. So when one has to compete with a female counter part for her mate, this can not only be tricky but turn out ugly if you know what I mean. For those whom have met the best friend or not, does infidelity ever cross your mind because you know this person is of the opposite sex? (weather attractive or not) What about for those quote "best friends" whom call at funny hours or the ones that call upon your man to do every task they have. Let's say your mate says she has a man, does it make a difference then? Well, all I know in today's society I wouldn't put nothing past nothing.