I don't get why cheating is wrong frankly, so have you ever cheated on your girlfriend and not told her?
Most Helpful Girl
Well I'm a girl so I've never had a girlfriend or cheated on one XD
Anyway in my point of view, cheating is wrong because when you have a relationship, you love and trust that person. When that person you love cheats on you, you feel all hurt and sad that the person wasn't happy enough with you and needed someone else to be pleased.
So to get to the point, if you love someone, you'd be happy with just that person's presence and wouldn't even think about sleeping with someone else. So I'd say your girlfriend right now, isn't 'the one' since you actually thought of sleeping with someone else, knowing her feelings would be hurt.