Both males and females find other people attractive while in a relationship, whether they're simply admiring them or thinking about them sexually.
I had a conversation with a female friend about how I knew a chick in high school and how that chick texted me about getting off to my pictures on facebook, she obviously wanted to bang me while being in a relationship, her excuse was that her relationship was edgy. Now my friend tells me, most of her friends from university have cheated on their boyfriends but never confronted their boyfriends about this. When a male cheats, he will most likely he will confess if he really likes her. Besides, girls go crazy if the guy cheats, she'll do everything in her power to make sure the current female he's banging is insulted.
Moral of this cool story, every girl is a whore until proven.