I think everyone is born to deceive in some type of way, either extreme or minor (I didn't take the cookie!). Cheating on a partner is just an extreme of that.
My husband and I are very flirtatious people. Constantly joking and 'hitting on' others. He's always telling me who he'd sleep with, and I tell him who I'd sleep with, obviously if we weren't together. I would NEVER cheat on him for ANYONE. Mainly because I don't want to mess up our relationship.
I'd say I was born a cheater, but in a very small amount. I did cheat on one of my boyfriends, but I felt so guilty about it I broke down crying and told him about it the next morning. Thankfully he was understanding and we are great friends to this day.
I don't think "love" has anything to do with it. If you are in a relationship, you don't exactly have to love that person. It's all about if you are LOYAL or not. If you are loyal and are happy, there is no reason to cheat, IMO.