By now, you know I don't buy it.
I've known many a faithful guy who had his heart torn out by a faithless woman, and vice versa. Some biologists claim that men are hardwired to look around, if not cheat, while women in relationships are programmed to tuck their eyes back into their heads.
Which is nonsense.
Let's be mature about this: Once you fall in love, other attractive people will tend not to fall off the planet. You will probably notice them some of the time, or all of the time. The trick is to treat your guy the way you'd have him treat you. You don't flirt with other men, ogle other men, carry on about other men, or sleep with them, either.
That said, you should expect the same treatment from your guy. Some women and men insist that men are incapable of fidelity, but Manslator Jeff Mac says otherwise.
I say we listen.