It's one thing to fantasize about your SO's friends, but it's another to deliberately look up their myspace profiles, download the image and save it into your porn folder for later use. That's crossing the line for some people, especially for those in a young relationship where trust is still being established.
I know my hubby sometimes thinks about other girls when he masturbates. Duh. I occasionally think of other guys when I get off. I'm pretty sure he's masturbated to thoughts of my friends, and I really don't care because I trust him. I know he's not going to act on those fantasies which involve other women, just like I'm not going to act on my fantasies involving other men. I'm very glad to have found a man that I can trust so completely