The age range 15-25 years constitutes the peak sexual drive and capacity for a male. The drive for sex is very powerful during these years. Sexual drive, like other basic drives for food, water, safety, etc., is recurrent and tends to occupy the person's mind till it is satisfied. Since social sanctions, health risks and emotional hazards all militate against sexual activity with another person before marriage, the most common way out is through masturbation. This gives relief, but only for the time being. Like other drives/appetites, this also crops up anew after some time and demands to be attended to and satisfied. While masturbation, even when repeated and regular,is no way equal to sex with another person, it definitely slakes sexual the thirst for sex on a periodical basis. This is a great help, as it allows to person not only to keep his sexual activity from going out of control, but also allows him to concentrate on his routine life and carry out his work without undue distraction. Preoccupation with sex, especially concerning someone you have so much contact with for several years without full sexual activity, is quite natural. It is certainly not a disease, though it can play havoc with your concentration and work if not resolved effectively

Just realize how damn lucky you are! Don't indulge in thought, if you must, practice meditation to clear your mind. I know many people who improved their personalities greatly by simply meditating for an hour or so every day or two.