Scarlett Johansson - who is romancing Josh Hartnett - says it's even more difficult not to stray as an actor because Hollywood is so incestuous and your acting alongside sexy actors.
The screen beauty revealed: "I don't think human beings are monogamous creatures by nature.
"You have to put a lot of effort into a relationship with somebody. People cheat for different reasons.
"I also think it's hard for actors generally just because having a relationship with somebody on the phone is miserable."
Scarlett, who starred alongside handsome Jonathan Rhys Meyers in new movie 'Match Point': "It's difficult to say to your lover, hey, guess what, I'm going off with this really sexy guy to do this very sexy movie but I love you and I'm going to be thinking about you when I'm rolling around in bed with this other person.
"Also a film set is a very incestuous kind of place. I mean you've got the makeup artist sleeping with the DP who is also sleeping with the wardrobe person."