I had a friend like that once as well. Claimed he never jerked off. One time when he was drunk he told us that he was lying. NO KIDDING! I think you would go feakin' insane if you didn't release the tension one way or another especially when you are at your sexual peak as an 18 year old. I once heard an interesting statistic about this:
98% of all men admit that they masturbate regularly. The other 2% are lying.
Yeah, I know. It's an old joke, but unless there is something seriously physically wrong with a guy, I don't know how they could not jerk off or have sex. Sexual desire is as natural as breathing, eating and sleeping.
I still masturbate daily and I'm 40! I've been doing it since I was 12. I would go crazy if I didn't do it. I get wicked cases of "blue balls" to this day if I don't get off. It sounds funny, but as every guy knows, blue balls are incredibly painful and is nothing to laugh at. The only way I can relieve it is by masturbating. My wife knows I do it, and she's cool with it because I have a huge sex drive and she doesn't.