The wisdom of this world is going to lead you into spiritual rebellion and earthly misery. Don’t listen to idiots who tell you that it doesn’t matter what the contents of your sexual fantasies are. It most certainly does matter. Your mental focus has an enormous impact on your relationship with others, your relationship with God, and your future happiness. God says that the only person you should ever be having sex with is your opposite gender spouse. If you’re married, having sex with anyone else with your mind or with your body constitutes adultery. If you’re single, having sex with anyone else is fornication. God detests adultery and fornication. God tells us to stay away from these things because He put us together and He knows that these things will harm us. If you load the gas tank of your car with gravel and then turn on the engine, you’re going to end up with some very expensive repair bills. If you blow off God’s guidelines about your sexual fantasies, you’re going to end up paying for your rebellion with some serious internal misery. God will not be mocked. If we repent of our bad attitudes and sincerely ask Him to have His way with us, He will bring great blessings out of our struggles. But if we chose to defy Him by ignoring the things He has taught us, then we will be disciplined accordingly. God is not some spineless parent who needs us to like Him. God is the King, and He won’t put up with our snarky “I don’t care what You say” attitudes. God spanks His kids and He avenges Himself on those who dare to spit in His face. So don’t go there. If you know you’re heading down a wrong road in the area of sexual fantasies, start talking to the Holy Spirit about it and ask Him to help you get back into a good place with Him.