well first congrats on being normal. We all in one way or another think about or plan what we will do and say to people every day of our lives the key is to be restrained in acting on our thoughts. We think about what we will say if he or she says this or that. we plan entire conversations out and encounters in or heads so to say that a fantasy is wrong well I cant. Most people are allways sizeing up someone or something from cars and jobs to people its normal to the exstreme. Futher let me say that looking and doing are two different things. The old saying is that just becuse im married doesnt mean im dead. just be kind enough not to look at and think about the opposite sex while with your gf, If you find this hard then and only then evaluate your relationship.