By having children. Seriously, once you have kids, your whole thought process changes. Time is limited, and quite honestly, you would rather sleep in bed than get it on in bed. Plus witnessing the whole child birth process makes you look at women's areas in a whole new light.
There are medicines you can use to decrease sex drive. They reduce testosterone levels. If you wish to truly decrease sex drive, you can have an operation to reduce testosterone production.
1. Have sex more often, which decreases the fantasies of it. 2. Eliminate all pornography from the environment, because that drives thinking and fantasizing about it.
You can cause a guy's urge for sex to lower by talking too much. Guys get tired of girls yakking about trivial things. They especially don't like complaints about their family, even if the girl is right!