How do you keep a girl from cheating?

Unfortunately if that option ever comes up for her she is the only one that can make the choice not to cheat - you cannot control her feelings or decisions. While dating her be yourself, be attentive to both your needs, treat her with respect as she should you, be trustworthy, loyal and always keep your lines of communication open. There is no room for games, negative jealousy, controlling, verbal or physical abuse, blame placing, ignorance or petty behaviour.