I think about this subject, being a healthy, single, young man and a virgin whose not yet ready for marriage but will consider it.
I think having these fantasies are somewhat natural, for men and women, as they are anticipating what may happen to them later in life, particularly if it’s something they want or aspire to have. It’s a part of them that wants to feel like they have something before they actually have it, so that it makes searching for a spouse more exciting and encourages them not to give up the search and to leave it also in God’s hands. Imagining the martial act in and of itself doesn’t seem sinful as it is just one component of a healthy marriage. At any other time, you might fantasize about your future wife’s cooking, and how you look forward to it, with her having you sample it from a spoon “say ahhhh…” sort of cute daydream. Things like this are harmless, but if they’re turning you on you should probably stop because they’re becoming disorderly, and if you find yourself focusing too much on the sex, then you would be seeking it for sexual gratification, rather than viewing it, in your mind’s eye, as an observation of what goes in in a marriage. When lust becomes involved in a daydream or fantasy, you’ll know it.
Obviously it can go in that direction very easily if you allow it to, especially with how the media has brainwashed society and bombarded it with improper sexual stimulation. That we are sexually stimulated, though, even by proper courtship and marriage is just part of how the brain works. God intends for these things to be pleasurable, because He intends for us to look forward to the way of life, that of the married life, that He has or will eventually open up to us. In wanting it to be unitive, He allows it to be pleasurable, even just in thought because He knows this makes us happy or comforts us in some way. Yet, at the same time, He wants us to realize that in order to have that, we have to behave.
But you just know the “other one” is waiting for you to think “I can’t take this anymore” and you masturbate or whatever to give yourself a release from the fantasy. But then you can turn this into something good too, because if that’s your problem then now you realize where your personal limit is. If even just imaging sex with an imaginary wife that doesn’t exist leads to masturbation, you know to do less imagining in the things about the marriage that are sexual or sensual and that you need to focus more on the whole of the marriage. If imaging martial intimacy still tempts you to sin, then it’s obviously a no-brainer- don’t do it, or when you feel the tingling down there it’s time to stop, wake up, and get back to work or whatever it was you were doing.
Also, if you are having these fantasies with the intent to be turned on, then obviously it’s sinful perhaps before even committing to the fantasy, since the intent is there to have it go in that direction. I can’t speak for anyone else, and I’m still young (26), but this just seems like common sense to me.
