Masturbation is self-stimulation by touching the genitals to produce an orgasm. To put it crudely, you're imagining you're having sex.
Many teenagers masturbate, it is very common.
They have a guilty conscience. Then you get into the hard-core, but you still aren't satisfied. Eventually you end up going out and raping someone because imagination and reality have become one. It may sound like complete rubbish, but it unfortunately does happen. This strains relationships, because, surprise surprise, your wife may not want to lie on the kitchen table like some actress in a film.