Be Honest - how many married people fantisize about there friends wife / husband?

Honestly? Never. Never ever. Not my friend's husband, not my BIL, not my husband's friends. No one but my husband. Every minute spent on fantasizing about someone else is a minute I'm taking from my husband. It's a waste of my time. I don't allow room for other people in my marriage-- even imaginary encounters.

I am married...

I am a dirty ba$tard horn dog that loves women....That does fantasize about nearly all sexy women!

But I have never had any fantasy of any of my friends wives.... And they are attractive....

yew. my girlfriends' husbands are so appaling. yew. never. my boss on the other hand is a handsome hunk i wouldn't kick out of my bed. but u do not f''k where u work. so the answer to your question - yew, no!

Why they need to do it if they're married?

I have actually had sex with a few of them.