Pleasure that is tied with truth has a lasting effect and can help make a Mitzvah more whole, like when we enjoy theShabbos and Yom-Tov meals. But pleasure that is tied to falsehood, like spilling seed, doesn't last. That's why when the pleasure is over there is no feeling of fulfillment. And that's why one doesn't tell those who want the best for him --those who love him-- about it, because he knows that it was just there to damage him, unlike the pleasures connected with truth which are there to make a Mitzva more whole. And that's also why one who does these things, always wants it again and again. Why? He just had it! If it was a truthful pleasure, why isn't it there anymore? The reason is because it is falsehood, and it leaves a feeling of void in its wake which causes him to search again to fill the void with another false pleasure.